Vapour barriers in renovation
Hi all,
I thoroughly enjoy FHB, but this is my first time posting on the forum.
I am currently renovating my family room, turning it into a new kitchen. The drywall is off, and I am planning to improve the insulation as part of the reno.
The house was built late 1970s with 2×4 exterior framing. Insulation is fibre glass with a black tar-paper like backing on the interior side – typical for that era.
To accomadate thicker insulation, and to work around a fireplace I demolished, I am planning to add 2x2s on the interior side. My question is, do I leave the existing insulation in place, and add a thin layer between the 2x2s with a new vapour barrier on the interior side – or will moisture then get trapped between the tar paper and the new vapour barrier? Or should I remove the old insulation completely, and replace it, finishing the job with a new vapour barrier? I could always reuse the old stuff somewhere else – like my basement headers.
A related question, the area where the fireplace was will be difficult to insulate. With the addition of the 2x2s I will have between half an inch a three inches of space to work with. Is spray foam insulation my best option? Is that a DIY project, even for a small area? I do not really know much about how spray foam is applied.
Charles, Ontario, Canada
Replies
Take out the old fiberglass and throw it away. Find a contractor who will blow cellulose in that space. BIBBs system or similar, there's another current thread with a post from a guy who describes the system of stapling and gluing a fabric to the bare studs, then blowing cellulose in there. Instead of or in addition to the 2X2 add-on studs, also consider adding 1/2" or 3/4" sheets of foil faced poly-iso (Thermax is one brand) nail it to the studs with shingle nails or button-head nails. Tape the seams with tape spec'd for the purpose (I used tyvek tape).
That would be one way to do this in a heating climate.
I don't like "blow-in" in the walls. After a year or two, it settles leaving no insulation at the top. Heat escapes through there like crazy, 'specially in our Canadian winters. And heating costs have gone thru the roof!
Just my opinion
locolobo; Edmonton, AB
Like you suspect you must not apply an additional vapour barrier over the existing one. You will trap moisture and produce trouble.
There are several options.
The first option would give you the following total R-values. Existing fiberglass R11 + 1½" extruded polystyrene (like the blue or pink stuff) R7.5 for a total of R18.5, or with polyisocyanurate (the foil faced stuff) R11 + R10.8 = R21.8.
The second option would be R18, or if you went with high performance fiberglass you could get it in R21.
If you went with the first option I'd recommend against using 2 x 2's and put the foam right over the existing studs and all (after slicing up the vapour barrier) as another person suggested. That would eliminate some conduction the wood would have provided and give you slightly better performance. You'd just use longer screws in the drywall and screw right through the drywall and insulation into the existing studs. Don't use screws that go into the studs more than about an inch. Longer screws would "conduct" more cold from the studs to the wall surface and over time you'll get little tiny black spots on the wall caused by dirt collecting on a slightly colder spot where the screw is. This is more likely to happen if you burn candles. Even with proper screws you might get a bit.
If you went with the second option you'd have some conduction through the studs, but it is a real common method of construction.
The US Department of Energy recommends R18 for walls in the coldest parts of the US, unless you have electric heat. I don't know the Canadian recommendations, but both options above put you about right. Since you are only talking one wall a slight difference between them is of no consequence.
Two part sprayed foam will give you more R Value, and it won't settle.Vapor Barriers are controversial. In cold weather climates it typically goes against the warm wall, e.g., on the inside, next to the studs.However, in very warm climates, many folks like to have the vapor barriers against the studs on the OUTSIDE of the home, so some from Texas have told me.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Thanks for the responses.
Another factor to consider is strength of the wall, since I am hanging my kitchen cabinets off of it. I'm concerned about whether or not 2x2s alone are strong enough. I think given the strength concern that I am best to screw the 2x2s to the existing studs and make sure they are good and solid. Not the best thermal option, but I don't want my cabinets falling off the wall either.
Sounds like the best option, particularly if I want to do the work myself, is to remove the existing insulation and re-do the wall properly, as a 2x6 wall. Since the rest of the house will still be just 2x4 walls (i.e. R12 at best), my longer term plan is to put 1.5 inch styrofoam on the outside when I go to change my siding in a few years. That will help considerably. In the meantime, I can use the old insulation in my basement headers, which are very poorly insulated.
Any thoughts on the fireplace? Is there a viable DIY option, or is spray foam by far my best option there. It is a small area, but with the brick hearth and cosmetic portion removed is it very irregular and not very deep.
Another question .... any good references out there on wiring into gaskets around the electrical boxes on the exterior wall. I know how to seal off the vapour barrier to the gasket, but what about the wire going into the gasket. Do I seal it off with a bit of acoustic sealant, after the electrician is done?
Thanks,
Charles
Re: the sealant around the wires...we used that grey electricians putty that comes in a plastic wrapped bar. Pull off a piece and press around the wire penetration from the inside of the box.
In a heating climate with your situation, I repeat advice to place Thermax or similar foil faced poly-iso foam boards against the stud then sheetrock over that.
If I use say half inch poly-iso between the studs and the drywall, will that compromise the strength of the wall ... note my concerns about strength for installation of kitchen cabinets. Or do I just compensate with longer screws?
I am familiar with the use of poly-iso on the exterior side, but not on the interior side.
Given that I am planning on some rigid insulation on the exterior, within a few years when I go to install new siding, is it worth the extra expense now to put poly-iso on the interior side?
Charles
Strength won't be a problem with cabinets, since the bearing surface is so broad. Just use longer screws. Only time you'll even notice that there's foam underneath the SR is when you mount something like a bracket for plant or shelves right onto the sheetrock. Then you can compress the foam and maybe get a SR screw or two pop out.
The poly-iso is not an expense that you'll even feel as a % of the $ that you'll be spending on the kitchen project. It serves as a vapor barrier and alot of R-value for the buck, plus cuts way back on thermal bridging. The foam on the outside, I think, should be unfaced extruded (the pink or blue stuff), which is a bit permeable.
The electrical boxes I'm thinking of have a flange around the face with a very thin foam gasket. The drywall pinches the plastic sheet between the back of the drywall and the gasket forming a seal. Then you just cut out the plastic over the box. The openings where the wiring enters the box have little foam rubber seals that seal around the wire when you poke it through.
I think I bought my boxes at Cashway, but it's been 5 years now.
Thanks,
I'll see if I can find boxes like that. Might be simpler than installing normal boxes with the plastic seals outside them, and might provide a better seal. Considering the price of fuel right now, a little extra expense in the insulation and air sealing may pay for itself pretty quickly.
Charles
If you are planning to add foam on the outside, I don't know why you are planning to add 2x2s and change the insulation at all. However, if you are intent on increasing your r value, while retaining structural integrity for hanging cabinets, why not run 2x2s horizontally with 1.5 rigid in-between? Running the 2x2s horizontally will reduce thermal bridging tremendously, as will the foam. This is a technique that I saw a lot of while working in the Yukon. It makes for very warm walls. Even in the extreme north.
Hmmm ... I like that idea.
The 2x2s need to be added because of the fireplace demolition. The wall is not flush, and the provide clearance in front of the old fireplace, I need to add thickness to the wall. Otherwise, I would not be adding them at all. The other exterior wall in the room will not have 2x2s added.
Adding the 2x2s horizontally makes a lot of sense. I just have to plan them carefully to account for where the tops of the cabinets will be, and where the electrical outlets will be. I could even use a 2x4 rather than a 2x2 at the level where the upper cabinets will be attached.
The question then would be ... what do I do about the vapour barrier? Would I need a new one, inside the rigid insulation. I guess if I use poly-iso I don't need a new one, but what about the one that is already there? Do I then risk trapping moisture between the poly-iso and the existing tar paper vapour barrier? Or is the porosity of the poly-iso such that the existing vapour barrier becomes irrelevant?
Charles
I'm too young to know much about the old insulation you have - I've sure ripped a lot of it out on renos, though! I don't really think that the old stuff was all that air tight. You will have to access that yourself. I think that you could probably just use regular blue sm over it all and put poly up over the sm and 2x2s. (This is how we did it up north). You could also replace the old stuff - the cost would be quite small. Blown-in systems are great, but they are expensive compared to batts. And since you need the 2x2s anyway, then you will end up with a good r value. And you're right - 2x4s would work well too. Try using 3 inch deck screws - they're strong. Kitchen cabinets don't way near as much as people think. Two screws will hold an awfull lot of shear weight.
Rip out the old fiberglass. Use cellulose. Wet spray or dense pak - the cellulose WILL NOT SETTLE.
Read up on cold climate building practices; books by Joe Lstiburek.
Make sure you do not trap moisture inside the wall cavity.
Thickening up the wall is a good idea. If it were me, I'd use 2x2 on the studs and have cellulose wet sprayed in the wall. Or stagger more 2x4 studs between existing wall studs so that there is a thermal break. Air-seal all gaps and wire holes before insulating. Spackle/tape the new drywall well. Apply caulk where the drywall meets the floor and around the windows. Use good quality PVA drywall primer - 2 coats. Apply 2 coats of good quality paint meant for kitchens/baths with the mildewcide alreay in the paint.
Mike Smith's "Mooney" wall might be right up your alley.
I think my introduction to the Mooney was:
http://forums.taunton.com/tp-breaktime/messages?msg=44500.119
I think this is where he discusses the genesis of the idea:
http://forums.taunton.com/tp-breaktime/messages?msg=37618.23
jt8
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