need help constructing hot tub room
Hi Folks,new to breaktime. I want to construct a hot tub addition onto my house. I am concerned about the moisture during the cold months, as this will be totally enclosed for about 6 months of the year. (during milder weather I hope to have it be a screened enclosure). I live in zone 4 and this past winter I had 4 feet of snow up against the house for the duration. What do I need to do to manage the moisture during those colds months? The addition will be approx. 8′ x 12′ and will be exposed to the outside on 3 sides. Will something as simple as a bathroom fan mounted in the ceiling suffice? I will be building this on a shallow frost free foundation with mostly gravel and then large pavers placed on top for support. Your suggeations are appreciated.
Replies
Hot tubs usually have insulated covers, don't they? They snap down around the edge of the tub, as I recall. That takes care of most of the humidity, except while the tub is being used.
"except while the tub is being used. "And why have a hot tub if you aren't going to use it?
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And why have a hot tub if you aren't going to use it?
Thing is, none of the privately owned hot tubs I've installed ever got more than occasionaly use, from what I've heard, so the cover is on almost all the time.
Using the tub for twenty-thirty minutes doesn't amount to much more evaporation than what comes from an extended hot shower or several showers in quick succession.
I've never owned or installed one, but the ones I have experienced were well used and lots of signs of humidity damage in the room.
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That's probably when they don't use a cover, I'd imagine but I've never been back to see any of my installations so I yield to your experience.
No -0 I meant to yield to yours - why I stated my lack thereof.I only meant to point out that it is a function of how much it is used. Somehow, it struck me that your first comment assumed that the cover would stay on.Where I saw problems was families that liked to get a lot of use, so the cover would be off a couple times a day and sometimes for hours
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Yes- most have covers and that will help, but with daily use, I still think moisture will be an issue. When I take a shower for 10 minutes, it is an issue- I can imagine spending 30 minutes a day in it (just me, not including my other half using it for her 30 minutes) and we might use it more than once a day too.
You might use it that often to begin with but most people find that spending more than a ten-fifteen minutes in a hot tub saps their energy. It can be dangerous for people with health problems.
Water is twenty-five times denser than air so it's effect on body temperature is likewise more intense.
Ten minutes is about the max for relaxation, unless the water temperature is reduced significantly. In that case the amount of vapor coming off the surface would also be similarly reduced.
Nonetheless, what it comes down to is whether the cover is kept in place during time it's not in use. If it's not the tub will definitely effect the atmosphere and the temperatur of the room and the home.
I installed my Hot Tub two years back and decided to place it outside on a paver patio. Main reasons for an exterior tub is: nothing better than snow falling while using it and also I didn't want to control the intense humidity, condensation and smell of having it attached to the house.
You never get cold. The water is 104 deg. and the steam/fog coming off the water keeps the face warm, The ambiance is great. Easy to get to the snow and roll. The only down side to outdoors is the run to the tub and ice buildup. many people solve this with heated patios/decks etc. or toughing it out.
If you must be inside, a common bath fan will not even touch the humidity problem. I've heard of ceiling fans being used and opening all windows after getting in the tub. Some cross ventilation would help and using a box fan type window exhaust. Consider vinyl windows too as the condensation on the windows could be a problem. Make sure the cover seals well.
Would also consider using Bromine instead of chlorine as the smell is not as strong and ozonizing the water helps.
What brands are you looking at? I got a "Sundance Optima" I and the family are very happy with it.
I will be building this on a shallow frost free foundation with mostly gravel and then large pavers placed on top for support.
That doesn't sound like a very good idea, actually. Hot tubs are heavy. Really heavy. Those pavers are gonna crack all to hell in no time flat.
You need to do the foundation right. Footings below the frost line and the whole nine yards.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
Lots of people here just put their tub on a bed of clear crushed gravel. There are no real point loads. Most tubs weight about 3000 lbs with two people in them. That breaks down to around 50 lbs a foot. No where near what a car exerts on a paved driveway.
(Edit based on Sundance spa weights)
Edited 5/24/2008 8:53 pm ET by fingersandtoes
In my neck of the woods, ledge is just below the soil surface (like anywhere from 2- 18 inches below) so to keep my project manageable for me to accomplish this summer, I was going to excavate to ~ 18-20 inches and if I uncovered ledge, leave it alone and fill around it with gravel. After my shallow, permanent wood foundation was set, (and "frost proofed") back fill with 3/4 gravel to about 4 inches from the top, put down pea stone and set the pavers into the stone. The reason I'm not just putting in an outdoor patio is because of the snow removal I will have to be doing. I just dealt with a lot of snow this past winter; it is not unusual to get several feet here, I'm in the snow belt. I want to be able to get in the hot tub after doing all the other physically demanding work I do, not add to it to enjoy the tub. and yes, I expect to be using it daily. and it will not be a party tub- this will be a tub for 2 max- not as big a load and not as many gallons of water to fill it.
If the bedrock is only 18-20 inches down, you're laughing. I thought you were going to have to go down 48 or 60 inches like we do up here to get below the frost line.
Dig down to the rock, drill in some rebar stubs to key the footings, and pour 8"x24" footings right on the bedrock. (You might want to look at the new fabric concrete form material Ron Budgell describes in his current thread, http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=104945.53.)
Once you've got those footings down, you can pour a single 12" frost wall right up to 12" above grade and build your stud walls on those. It won't cost you much cubic because your f-wall height will be so low.
You can then fill with ¾-clear gravel, vibrate it, and pour a 3" slab. That way, you won't have to isolate the tub from the building around it to prevent stress fractures when the tub eventually settles on the gravel bed (as it eventually will if you do it your way).
Note that if you have ground-water issues, put a piece of 4" pvc DWV pipe in the footing form on the downhill side of the rock slope to allow any water that gets under your slab to find its way out. When you strip the forms, fill that pipe with ½" gravel and cap it inside and outside with geotextile and galvanised ¼" wire mesh.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Do you mean "frost protected" foundation? Nothing wrong with that per se, but supporting a hot tub on pavers on gravel sounds hokey.
You are right to be concerned about moisture damage, especially in your roof, ceiling. More than once, I have been in motel hot tubs and looked up at the water damage in the ceiling. If you can afford it, spray foam would be a good way to go. Otherwise, carefully detail your vapor barrier--tape the seams, caulk top and bottom plates, etc. I personally would use a layer of foil faced polyiso as a vapor barrier.
Yes, absolutely get a vent fan, and get a good one with plenty of capacity. Put it on a timer switch.
Just some idle thoughts ...
Normally, when we build, we do so in a way that tends to place a moisture barrier on the outside of the house (felt or tyvek) and a moisture barrier on the inside face (kraft paper) as well. This construction seems to assume that moisture will be coming from the outside, trying to get in. This seems to be setting the stage for moisture to become trapped in the walls.
Before I go any further ... before you build, go over any solutions with your building department, as I fear they will tend to object to any unusual solutions you may try.
Now, rather than trying to keep moisture out, let's take another approach ... let's assume moisture will get in there, and give the moisture a way out!
Here's a wall construction that I've never tried, and have only now thought up:
From the outside face, in ... lapped vinyl siding. If wood is used, make sure to back-prime. Have the siding set up, off the sheathing, with thin lath. I think even 1/4 strips would be enough.
For sheathing ... pegboard. No paper or tyvek over it.
Wood framing ought to be OK, but using light steel will remove warping as an issue.
Foam panels as insulation, being sure that there are small gaps at the bottom. Maybe use soda straws as spacers. This gap is to serve in a manner similar to the 'weep holes' in masonry walls.
As long as there's still a gap between the foam, and the face of the inside wall, I'd cover that with the same sorts of substrates you would use for a shower.
The final facing would be either FRP (the pebble-grained plastic you see in commercial kitchens), or even sheets of Formica glued to the wall.
In many ways, the foam insulation will act as a moisture barrier. I'm counting on the moisture condensing there, and flowing down to the bottom of the wall. That's the reason for the gaps, and the spaces at the bottom ... let's give that water some place to go. That's also the reason for the pegboard sheathing: ventilation.
You're kidding, right?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I was pretty clear as to my inexperience ... if there's more substance to your objections .... please explain, so we all can learn.
I was pretty clear as to my inexperience ... if there's more substance to your objections .... please explain, so we all can learn
Okay, sorry. It's so far from reality I really wasn't sure if you were kidding or not. Let's take it a few elements at a time.
Normally, when we build, we do so in a way that tends to place a moisture barrier on the outside of the house (felt or tyvek) and a moisture barrier on the inside face (kraft paper) as well. This construction seems to assume that moisture will be coming from the outside, trying to get in.
You're labouring under a few different misconceptions here. Felt is waterproof, and could be considered a moisture barrier, but Tyvek is not. It is designed and sold as an air-barrier. It's purpose when applied to the outside of a building is to stop wind or negative-pressure induced air infiltration (drafts) getting into the house. Further, when builder's felt is applied to the outside of a building, it does not act as a true vapour barrier because it is laid in shingled rows and presents no obstruction to air-born water vapour, only to liquid water which it shunts out and down under the siding.
Second, in most temperate regions we do not normally place a vapour barrier on the outside of the building, because that would trap water vapour coming from inside the house in the wall system and cause condensation in cold weather. The vapour barrier--aluminised kraft or polyethylene sheeting--is placed on the inside of the building wall, to keep human-generated water vapour (showers, cooking, laundry, etc.) out of the wall cavities.
Third, we don't assume 'moisture' is coming from the outside; we assume liquid water will strike the house and we build so as to shed that water by shingling exterior coverings appropriately. Roof and wall coverings are not conceived of as waterproof elements (with the exception of flat roofs, which do require a covering which can hold and retain water until it drains or evaporates); they are designed and installed as water-shedding assemblies.
From the outside face, in ... lapped vinyl siding. If wood is used, make sure to back-prime. Have the siding set up, off the sheathing, with thin lath. I think even 1/4 strips would be enough.For sheathing ... pegboard. No paper or tyvek over it.
Siding is commonly laid on 1x3 furring, so your idea of using ¼" strips to allow air flow under the siding isn't that far off base. But sheathing has structural importance in that it prevents a stud wall from racking. Pegboard isn't rated for that sort of service, and while it might work, it would take an engineer to sign off on it and a building inspector to agree the engineer hadn't been smoking funny cigarettes. I am not too sanguine about either of those possibilities coming true.
Wood framing ought to be OK, but using light steel will remove warping as an issue.
Light steel wall assemblies have even less structural rigidity than wood; when combined with your pegboard idea it really doesn't strike me as a winner. KD wood studs don't warp if they are properly chosen and installed; green studs can do so but if locked into a wall structure with proper interior and exterior sheathing, they won't. That said, few walls are built with structurally-significant interior sheathing.
Foam panels as insulation, being sure that there are small gaps at the bottom. Maybe use soda straws as spacers. This gap is to serve in a manner similar to the 'weep holes' in masonry walls.As long as there's still a gap between the foam, and the face of the inside wall, I'd cover that with the same sorts of substrates you would use for a shower.
You're trying to drain a wall which is designed to get wet from the inside. I understand that, but as explained above, the whole idea runs contrary to building practise. Even assuming you did construct this, the bottom plate of the stud wall would be constantly wet, as would the bottom several inches of the studs and pegboard, by absorption. The studs and plate would soon rot and the pegboard would simply disintegrate, thus requiring major and difficult repairs or replacement of the entire exterior wall. Brick veneer walls have weeps built into them to allow exterior wind-driven rain that gets behind the brick to get back out again. The builder's felt on the sheathing behind the brick veneer sheds this water and does not let it penetrate into the wall structure itself.
Further, the 'substrates you would use for a shower' (Kerdi membrane, for instance) would be superfluous to your design purpose as XPS foam doesn't care much if it gets wet. Considering how expensive such membranes are, they are not to be used without reason.
The final facing would be either FRP (the pebble-grained plastic you see in commercial kitchens), or even sheets of Formica glued to the wall....I'm counting on the moisture condensing [on the foam board], and flowing down to the bottom of the wall. That's the reason for the gaps, and the spaces at the bottom ... let's give that water some place to go.
But if you are 'counting on the moisture condensing [on the foam board]' inside the wall, why are you suggesting an impervious interior wall finish? By doing that you would invalidate your whole idea, faulty though it was.
Sorry, my friend. Nothing personal. I'm sure your heart is in the right place, but you need to get a few basic concepts straight. Hope this helps.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I greatly appreciate your explanations.
I appreciate you replies ... but a few items still puzzle me. I mentioned 'check with the building dept' because I was part of a job (building an indoor communal tub) where the inspectors had some concerns about the vapor barrier techniques.
These concerns seemed to have two basis ... first, the techniques being used were 'different' from what the inspector was accustomed to seeing, and secondly because of recent concerns over mold, etc - which, in turn, seem to have been the result of our last 'energy crisis,' where everyone wanted to make houses air-tight. Oops. While I understand your belief that wall sheathing provides shear strength to a wall .... I am puzzled by what I saw last weekend just over the hill (in California). That is, I saw plenty of two-car attached garages, with shear blocking only on the door face. The common wall was simply drywall, and the two outside walls had NOTHING on them but stucco. That is, paper, plaster, chicken wire, plaster, paint - all clearly visible from the 'inner' face of the garages. This was contemporary (appx 30 yr old) construction between San Francisco and Sacramento - prime quake country. Since a hot tub room is likely to be smaller than a two car garage, I wonder about the need for such shear plates (sheathing). I agree that my 'idea' was quite different from the way you build the usual bedroom. Then again, we're not building the usual bedroom, and I thought the differences were great enough to explore different methods. Water accumulating at the bottom of the cavities? That's why I specified spacing the foam panels up off the bottom plate - and why I suggested foam panels, rather than spray-in foam. Why did I suggest 'shower style' interior faces? As I see it, the point is to make it a difficult as possible for water to get in ... accept that some will get in no matter what ... then give that water an easy way to get out. I've seen far too much "greenboard' and 'bath grade masonite' turn into a soggy mess after a few years to place any faith in them for humid environments. I can't imagine the usual drywall and paint performing well in a 'hot tub room,' even if there is not the splashing that you see in a shower.
nice job explaining all that. I was thinking after reading the post you responded to , where do I begin and how much time do I have before diner."it aint the work I mind,
It's the feeling of falling further behind."Bozini Latinihttp://www.ingrainedwoodworking.com
...where do I begin and how much time do I have before diner.
Great minds think alike....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I wouldn't suggest trying to rely on your wall assemblies to handle excess humidity. If the air is the problem, deal with the air.
A bathroom fan will do. Get a good quiet one like Panasonic makes and wire it to a humidistat. Provide a source of make-up air - this can be as simple as a 1" gap under the door. The fan will vent air from the room whenever it is too moist, and if you don't have excess humidity, you don't have a problem. You aren't going to have more humidity than a bathroom with a shower, it's just that unlike a shower, the tub gives it off when you aren't there too, which is why the humidistat is important.
Since 1995 the code here has made us attach kitchen and bath fans to humidistats, and the reduction of moisture related damage in houses built since then is pretty obvious.
I've been folowing this discussion because it is an interesting challenge. I have not designed opr built one like this, but have thought of it for my own home.
I am also the kind of guy who never quits working - in that when I am on vacation or visiting and supposed to be relaxing in the hot tub, I am observing what was sued, how things were builkt, what went wrong, and how I might try to do it better.
This sort of project is really a challenge because it pushes systems and the principles we hold dear to the extremes. So in the same way that auto racing has brought about a lot of the improvements in the family car over the past hundred years, house additions like this that deal with heat and moisture and fenestration to the extreme cases prove or disprove theory.
I start with the assumption that you want windows and doors in this room. That means a point of condensation. So I would probably use vinyl or composite frames unless you have the budget for custom red cedar there.
The compacted gravel stone base sounds good to me. use superb insulating details at the perimeter, because you will splash, drip, and condense a lot of water to run into the floor and the ground under it. You do not want that water to freeze before it drains away or evaporates.
I would use only spray foam or EPS/XPS foam panels for insulation. Anything else in this extreme location will hold moisture, and I doubt that tyou will keep all moisture out.
I would use all PT wood and SS fasteners for framing and redwood/red cedar for trims and finish surfaces with again, SS fasteners.
In a warmer climate, it would be all masonry to the top of the wall.
I would use vapour barriers on the interior of walls and ceiling, furr out and then the finish surface.
I would detail window trim so as not to trap water running down the walls.
Then I would use a mechanical vent on a humistat.
I am not sure how I would finish the wood interior. I am sure somebody muist have dealt with this before.
A tight seal like a polyurethene could trap water to the back side more.
Mildew growth would be more of an issue with no finish, it seems. Rubbing oil would be a pain to maintain.
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Have you ever seen problems with a bathroom fan's vents becoming restricted from freezing in high humidity applications?
Seems like below freezing temperatures above the insulation would cause vapor to condense and freeze inside the duct tube.
That brings up another question that I've never dealt with; what happens when vapors condense, freeze in the duct, then later return to a liquid state? Doesn't the water run down the duct into the fan and motor, then fall back onto the bathroom floor?
Edited 5/26/2008 9:42 am by Hudson Valley Carpenter
Good questions while we are on the extreme edge.I haven't seen that, but maybe just never been aware of it.I slope my post-motor/fan ducting down and out but I have seen the soil stack pips frosted in tight, so it seems like you are right that it can happen for frost to fill it tight. you could bury the exhaust in insulation except the motor itself. I normally use remote location fans for the quiet, but ceiling mount would be better for this, i suppose.
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While I'm all in favor of ventilation, I am something of a skeptic. I've seen far too many exhaust ducts that were crushed, kinked, or run in a haphazard manner over long distances. Every one has had a healthy content of what I assume was dust - though it may have been growing.
I've also seen far too many exhaust fans that worked poorly simply because there wasn't enough fresh air supplied to the room. I suppose we have to start with "humidity happens," and go from there. Why don't we give it somewhere to go?
In my earlier post, I was trying to imagine a way to condense the water on the wall, then give it a way to drain out the base of the wall. I may have overlooked the obvious: the window. Won't the moisture tend to condenses on even a double pane window? If so, where does it go from there? Will it drain out / under the window to the outside - or just go down the inside wall? Can we direct that water into a pail, or a drain?
Thanks- all good suggestions. I have been wondering about the inside finishes myself. At one point I was also considering building a sauna, and have a couple of good resources to help me build one. In that case, the interior would be all port orford cedar- ceiling and walls, but there wouldn't be many penetrations like windows. For the hot tub, I definitely want to see outside and have a door to the outside. Make up air can come from a "plug" in the wall- sounds weird but if it is done for sauna's, it can be done for a hot tub room. Basically a hole in the wall that can be covered up to conserve the heat in the room when you're not using the tub and opened when you are in the tub and have the fan going. I will definitely get a tub with a good cover, and keep it covered when not in use.
My wife is REALLY sensitive to cold drafts, so that's what I'm thinking about while reading this.
The focus has been on pulling hot moist air out... but what do you replace it with? Does it come from the warm house or from the cold outside?
Obviously in the summer, you release the hot wet air into the outside by opening up a door or wall.
In the winter, warm slightly moist air is actually a good thing, provided you don't already have a whole house humidifier.
Just thinking outloud for grins here - please shoot me down Piffin or Dino - but what about an air exchanger system? If the idea is to pull out the high moisture of the air, then pass it through an air exchanger (exchange the temp with the outside air) and actually condense the vapor out. Set it to run with the fan only setting on the furnace, so it will mix the cooler slightly moist (now) air with the rest of the house. Pull hot moist air out, push in dry warm air. Duct it so it hits the windows to keep them clear.Rebuilding my home in Cypress, CA
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If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
An air exchanger is not that bad an idea. I did install just such a system for an indoor pool.
Though your understanding of the operation is a bit off. Typically, the inside air will transfer some of it's heat to the incoming air as it is exhausted - taking the moisture with it. Concern about make-up air is also well founded. The best exhaust fan can move only the amount of air that is supplied.
"My wife is REALLY sensitive to cold drafts"I didn't know cold drafts existed where you live
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You wouldn't think it!
In the summer, I have to beg her to open the door or window and let out the hot wet air. The funny thing is that 20 minutes later she's back in there getting doodied up and complaining that she's hot!Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
You shouldn't have any humidity problem. I'm in Maine, zone 5. Our tub is in an unheated room in the back of the unheated garage. When I built the room, I put in a fan, figuring I'd need to get rid of the humidity. I never need it. The cover keeps the moisture (and heat) in. We use it almost very day and just open the windows, even in winter.
Once you get a hot tub, it becomes one of those "I could never live without one" sort of things.
I am not sure how you were planning on separating the hot tub room from the rest of the house, but you most certainly do not want to be dumping large amount of humidity into the rest of the house (ie each time you use it). The cottage we purchased had a hot tub room on one end of the building with large sliding glass doors beside the tub (which we would often open in the winter when we used the tub). We are also zone 4, and we discovered during our first winter the very real flaw in not isolating that room, and allowing the humid air from the hot tub to enter the rest of the building. Over time, the humid air ended up passing through (perhaps a poorly done.. or compromised vapour barrier in our cathedral ceiling) and froze on the underside of our steel roof.. which of course later thawed and caused a host of other problems.
Bottom line is be certain you are properly dealing with the sudden, and significant bursts of humidity your hot tub will throw off.
Thanks for the heads up- I was planning on enclosing it, with a door between it and the rest of the house, but not a big glass slider. I think I really need a good fan to draw the moisture outside. Did your hot tub room have an exhaust fan?
Our glass slider door is to the outside, and the hot tub room was not "enclosed" from the rest of the building which was the problem. I just installed a couple of glass french type doors to isolate the room while being used and our humidity problem was no longer an issue. We usually open the slider door to the outside while using the tub so that we have the outside air feeling..and the humidity has a place to go. Our interior finish on the walls is western red cedar left raw. It has been there for probably 18 or so years and still looks great. No effects from the humidity on the cedar. No fan in the room. I should point out though that we do not leave the hot tub full of water at all times since it is a cottage for us. I suspect I would be forced to consider things in greater detail if it was functional all the time.
Ventilate!! It will cost you, though. Cost you more if you don't, though. Cover or not, this thing is going to generate some serious moisture and could destroy struture and finish materials in short order if you don't ventilate. There are so many issues associated w/ having one inside ... I always strongly recommend against it whenever possible.
I'm with the other guy ... put it outside. I've used mine when it was -20 degF ...
If you insist on putting it inside ... control a large exhaust fan w/ a humidistat (don't forget to maintain that sensor annually or it will go bad on you). Consider a heat recovery ventilator to reclaim the wasted energy.
If a hot tub sits on e.g. gravel or pavers and is enclosed in a good skirt, my guess is there will be little freeze/thaw action under that base. A hot tub is maybe roughly 4,000 lbs ... 250 pcf or <2 psi. Often minor movement of the tub should be OK if it is not connected to anything else anyway ... I would think. It ain't a house and it is different.