I will appreciate advice from experienced builders on building a deck for my son-in-law. He has asked me to build a deck on top of a wing of his house that was added by the previous owner. The wing was formerly for a swimming pool which was later filled in. The roof is flat built-up tar and gravel supported by massive steel I beams so weight is not a problem and the roof is flat.
We want to lay a floating deck on top so as to retain the waterproof roof that is there and provide a surface that is attractive and will not rot. Any water going through the deck will drain from the roof, but it will be damp/wet beneath the deck. My plan is to lay pressure treated 2 X 4 joists on the existing roof and screw the decking to the joists from the top. There will be no access from below.
We have considered the following options and we do not know which is best or if any of them will be suitable. Cedar will look good and is rated pretty good for rot resistance but is soft. Fir is inexpensive and strong but will it rot? Pressure treated lumber may be the better choice but any we have seen is not very attractive and we do not know what kind of surface finish should be put on it (if any). We are in a coastal pacific climate, rot is serious here. Advice on materials, construction, and other considerations we have not even thought of will be appreciated. Cost is a consideration but durability is of more concern. I will appreciate all replies. Thanks.
Sedna1
Replies
Most "built up tar and gravel" roofs are very thick and heavy, make sure it is capable of supporting the extra deck load, and dont forget to add in snow load if thats a consideration as well. that may be the reason they are massive.
Woods favorite carpenter
graveled BUR is barely more weight than shingles, sometimes less. A four ply would be 90# of paper and 100# of asphalt, then 40-80# for the stone. That's about 250# / square or so
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Most here are constructed with corrugated sheetmetal or other sheathing/substrate, the 8-10" of NASTY insulation then your mopdown paper layers then the gravel. Sounds like he may have bar joists for rafters if he is dealing with steel beams which is a VERY odd choice of materials for a room that used to house a pool.
im not sure where the rest of my first reply went, i had went into the pt preference as well. =) Woods favorite carpenter
Thank you to Mattswanger and Piffin. I wish to add that there is no concern about the load on the deck, it was overbuilt when constructed and yes we get occasional snow load here but usually melts within days so there is no build up. However it can remain rainy for months at a time. The built up roof does not have large gravel on it, the stones are not more than 1/4 inch, so it is pretty level. I am concerned about shortening the life of the roof. I had thought that protecting it from the sun would actually lengthen it's life so I would like to hear more about that.I will definitely get an opinion from a roofer about the condition. To my eyes it looks to be in excellent condition. The addition is considerably newer than the house but I think the actual age can be determined from taxation records. I have heard about Ipe but have never seen it and think it will be hard to obtain here. We are sort of in the backwoods I guess. We can get the recycled plastic planks. They are about four times the price of fir and double that of cedar because we are in a logging community and local species are very reasonable here. Another possibility is yellow cedar (cypress) it is priced about the same as Western Red Cedar but as far as I know its attributes are similar.Thanks for taking your time to help me,
Sedna
How big are we talkin' here? Area wise.Remodeling Contractor just on the other side of the Glass City
The purpose of the gravel is to protect the asphalt from the aging UV rays of the sun. There is a BUR roof that is smooth surfaced, but it needs to be recoated every five years to account for the aging. If you had a smooth surfaced BUR, you would be right that the deck would protect it.as for local species - any wood deck nortmally requires 18" of free air flow from under it to prevent excessive moisture causing rot from down under. The less air movement and venting you have, the more problem you see. It would not surprise me that in a humid environment/climate, a local species like that would be suffering in ten years.'course, then you could replace both deck and roof in ten years time.
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I was thinking that the paving if placed on the roof would just replace the gravel and perform the same function of protecting against UV light. As for moisture under the pavers - the roof is flat (almost) and holds standing water now in small puddles. I have seen BU roofs in commercial buildings that actually have water on them most of the time. There is some ventilation inside this roof as there are vents sticking up and I assume they were to vent moisture from above the ceiling and below the BU roof when this structure was used as an indoor swimming pool. Although I can't see the internal sructure it must have been originally designed to handle high humidity (as a swimming pool) but I guess it is not good to assume things in this situation. I guess I will have to open it from below and have a look.
Sedna
When I say rot the roof, I mean the roof, no the wood structure that gets vented under it. The asphalt can rot out too. There are micro-0rganisms that feed on asphaltwater puddling is not a good thing for any roof. Typical specs call for enough slope to drain it. There are indeed someommercial BUR roofs designed and intended to hold water for climate control purposes in soime climates, but those are subject to some VERY heavy duty specifications and detailing thatI doubt very much was a part of a residential BUR ver a pool. It would have cost twice as much.Since you normally have puddling, when you find out from your historical research how long ago this was buolt, add 15-20% for aging because of water puddling because that will shorten the life of the roof that much."the paving if placed on the roof would just replace the gravel "Stripping the gravel off is not an easy operation
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I guess I will have to open it from below and have a look.
That is when you will see if it is a metal pan or wood deck. At that point you need to take close look at the screw pattern penetrating the decking. BUR s use tapered insulation boards to achieve enough pitch for drainage. The board is screwed down with large appropriate length screw fitted with large fender washers at approx.2' o.c. That is the first place most BUR contractors skimp and save a little time and material. Areas where there are to few screws will oftyen shift a little durring the hot mop stage and the roof will later develope a bubble under it. It is hard to see bubbles in a BUR unless you have a lot of experience looking for them. One of the signs of numerous bubles is the development of puddles. The drainage pitch is interruped by the high areas and puddles develope. On wood deck roofs, if they follow steel pan decks, it is the area for leaks to develope away from any flashing points, but like piffen pointed out 85-90% of leaks in BUR occurre at the flashing.
The only way I know to get the pea gravel off a BUR is with a conrete cum-a-long and a flat scoop shovel. It is generally only done when the roof is being replace and damage to the mopped layers doesn't matter.
I use PT for the sleepers and Ipe for decking. Trex or other synthetic might be worth considering too. Use SS screws for fastening.
the bigger concern for me is the BUR roof under this since it is now surfaced with gravel. You don't say how old it is, but most at designed for 15 - 25 years and often last less than that. Adding this new deck over it will surely shorten the life of it.
And the normal way of placing a deck over a BUR is to install pitch pans around points of atachment, something that will take a skilled crew with a kettle.
If this existing roof is ten years old or more, the thing to do is to have i5t replaced first with EPDM rubber roofing at .60 thickness and then do the deck. We've had several threads with photos on this that you can find using advanced search for terms EPDM + IPE` and roof.
Placing a deck over an aging existing roof would be a shame if you had to tear it up in two years to replace the roof then.
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Where are you located? What are the neighbors using? Forget Fir. Dont even think about Fir.
Hi folks!
I guess I should have included more info in my first post. The deck is going to be 1000 ft2 and is located oceanside on Vancouver Island. Since posting I have been talking to some sawmills here and one guy told me it is nearly impossible to get old growth cedar as the big forestry companies are selling all of (and it is scarce) offshore as raw logs.
Local cedar is second growth which they tell me is little better than old growth fir. The problem is so many conflicting pieces of advice and each supplier has a profit motivation to push their solution. This is what I love about this forum. Each person shares their knowledge and no one has an axe to grind.
Thanks Sedna
Not sure if it's an option there, but on the East Coast here, alot of beach houses have roof decks. They fiberglass them. Not roofing, no deck. Just fiberglass on the sheathing. It's pretty tuff, and when installed right lasts a long time. If the roof turns out to be older and in need of replacement, it might be an option.
I just finished building my deck over a flat roof (1/4" slope per foot) covered with EPDM. My workshop is below the deck. My concerns were to have a deck that would allow access to the roof below if and when there would be a leak. I settled on Ipe tiles laid on a pedestal system. The pedestals are PVC and a type of plastic so there is nothing to rot. The tiles all interlock and form a great looking and long lasting deck that you won't have to worry about. When you walk on the deck you would never know the tiles are on pedestals. The tiles can be lifted up when roof access is needed. If you use sleepers you will have much more work on your hands to access the roof. You can also use concrete pavers since weight is not an issue. No maintenance at all with concrete pavers! I actually wanted to use the concrete pavers but the architect had a fit about the weight issue.
You can search for Tile Tech Pavers for the concrete pavers and pedestals and East Teak Hardwoods for the Ipe Tiles and connector pieces. I am not associated with these companies they just happen to be where I purchased my materials. If you want any pictures or more info let me know.
Good luck,
Dale
What a good idea. I never even thought of ceramic or concrete but it the deck can take the weight it solves all the problems. It can be attractive, no rot at all, can be taken up easily if the deck beneath should ever leak and can be pressure washed if it grows moss and all sorts of other virtues like non-combustible and scratch, and dent proof. I can see no down side except weight and while I said weight was not an issue this would be much heavier than I had even considered, but it would be worth getting an engineering opinion.Before I get too carried away - does anyone know of some downsides to this idea?
Sedna
Two big problemsYou absolutely have to have a drainage plane.You need to know how you are going to anchor your railing posts.
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There is no way to use pavers on this BUR without rotting the roof out almost immediately.
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"There is no way to use pavers on this BUR without rotting the roof out almost immediately."
http://www.envirospecinc.com/
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That is a systemdesigned to provide a drainage plane and not just lopping a bunch of tiles down ontop of a roof
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Here is what we used on our roof deck - it works great - http://www.kemper-system.com/OC/eng/flat-roof/
Jeff
Edited 2/4/2009 9:10 pm ET by Jeff_Clarke
How expensive is this material? How do you think this would work on a flat school roof that has many leaks?
Luke
Any time a roof is that leaky, it is a waste oftime to deck over it. You need a good roof first, then the deck.
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What would you suggest to a client that had a flat roof over their building and no money to re-proof. The roof consists steel trusses 4' oc struct/Insulated panel, felt, and hot mopped tar.
Side note......it is a new roof the company does not seem to be able to fix the problems........warranty is not possible.......suing is useless!
Luke
"no money to re-roof."Let it leak I guess.???Not necessary to re-roof most of the time unless it is totally botched ( which I have also seen)
Usually the leak is at a flashing detail or a badly set drain. Once somebody with knowledge and experience finds the source of the leak, it can be fixed.I recall a situation on a govt apt project for elderly where I and three other roofers bid in the neighborhood of 24K each.The winning bid came in at less than 19K
I was leaking within a year and the whole thing needed to be redone because of the poor workmanship those yokels had done on it
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Slight hijack - but follows your thoughts;
"Inspected" a house for a good customer coupla weeks ago. Talked to him after he recieved my "report of issues and concerns". Gave him a "top of the head " ballpark to give him an idea of what some of the concerns may ballpark out cost-wise.
One of the items - All of the sink drain assemblies/ traps - shuts / supplies were original to about 1950 - 60 and were severely corroded. Some already dripping/ leaking. Just the under cabinet type stuff.
Told him about a man day to r&r all five - 400$ and around $100 for mat. Figured I'd just redo all the under cabinet for that roughly.
Went there today to coordinate with the people who will actually end up living there. He throws down a copy of my "report" with the numbers that I gave him in the margin, over on the left. Over on the right, are the numbers from some other outfit with their "ballparks" ( I believe these were solicited from the seller, so I'm thinking there's some gamesmanship here)
Anyway, the other guy's notation was for $130. I'd be outta money by the time I picked up the materials and knocked on the door.
Told the owner to make him do it. Told him I'd come and watch the guy, make sure it was done right and take care of take care of all the hand holding for free just for the entertainment value.
HO is a good guy and got quite a laugh out of it this time.
Low bidders are big trouble for the people who take them.
That was just one of the 13 items, the rest were about the same....
...If it were easy, all the cavemen would be doing it...Remodeling Contractor just on the other side of the Glass City
Thank you to all who have contributed. The discussion and suggestions have been helpful. There are so many options but all have drawbacks of a technical or cost perspective. I do not under rate the difficulties of this job particularly in a climate where it can rain every day for months.
I have concluded the best option will be to lay a grid of pressure treated 2 x 4 raised on ceramic tile pedestals which I will glue to the existing roof deck with tar. This will be used to create a crown and the spaces below the 2 x 4 will allow free drainage of water off the existing roof, should any seep through. I will leave the existing drains in place. Then I will lay a pressure treated plywood deck on the 2 x4 sleepers and cover it with vinyl deck covering which can come with a 10 year warranty against leakage. I hope the pressure treated plywood will not rot from below. I will extend this new deck surface slightly beyond the existing roof and add new eaves trough to get rid of the water. The old roof should remain dry except for humidity and if a leak does occur the old roof is still there and hopefully intact.
I know this is not an elegant solution but it should be cost effective and hopefully will work. I would appreciate and analysis of flaws in this plan and suggestions on how to carry it out if the idea holds up to critical analysis.
I love the cermic or concrete tile on plastic pedestal suggestion but the cost is out of reach.
Sedna
have concluded the best option will be to lay a grid of pressure treated 2 x 4 raised on ceramic tile pedestals which I will glue to the existing roof deck with tar
When you glue your ceramic pedestal down with tar besure to spud back the existing pea gravel. Clean as much gravel off as possible and lay in you tar, then set your pedestal and srinkle the loose grave over the tar around the edges. You may need to wait a week or so before laying the 2x4 sleepers down, Depending on weather, it can take that long for the new tar to set and keep the peds from moving on you.
That is how I would do that too, but to expect a DIY with no experience to be able to remove gravel without causing leaks is reaching for the moon. it can be a pretty tricky operation depending on the type of asphalt used for the gravel and on the temperature at the time, and the age of the existing roof.So I would temper that and sy to just use a good stiff broom on that spot to remove loose gravel and not mess with the embeddded stuff.
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