Not Enough Insulation?
We have contractors working on a wood frame house and when we stopped by this weekend to check in we saw that they were already putting in insulation. The thing is, we’re worried that it’s not enough. Here’s the deal: The house is detached on one side. On that side it is exposed clapboard both…
We have contractors working on a wood frame house and when we stopped by this weekend to check in we saw that they were already putting in insulation. The thing is, we’re worried that it’s not enough.
Here’s the deal: The house is detached on one side. On that side it is exposed clapboard both inside and out. On the interior after the clapboard there is now a 4″ air gap, then a layer of plastic sheeting, and lastly a layer of R11 insulation.
Should they be tar-papering before the plastic sheeting? Is the air gap a trap for cold? And isn’t R11 a really low grade of insulation–we thought these days it was supposed to be 18 and higher? We just want the place to be really energy efficient. It’s an old house and so long as we’re gutting it, we want to restore it right.
Thanks in advance if anyone has experience with this!
This sounds like a bad wall assembly. Without a thermal break between the studs and the exterior wall you’re going to have thermal bridging. That’s a phenomenon where the studs, by being in contact with an exterior wall, conduct cold into the building. When this happens it de-rates the R-value of the insulation, so your R-11 will actually be more like an R-4 when taken in total. Also, in NYC, as with any climate zone that has cold winters and hot summers, you should really be putting the insulation on the outside of the building and it should be rigid foam (polyisocyanurate) or mineral wool. Spray foam is great too. You should also make sure that there is a continuous air barrier. If you do that, you can get an effective R value of over 21, which is what you want. For a good visual, check out the link I’ve provided here and scroll down to Figure 5 “Building Section”. Don’t mind the fact that it has a pitched roof. And do yourself a favor and read the whole article, starting with the first section.
Cheers.
http://www.buildingscience.com/documents/primers/plonearticlemultipage.2006-11-14.1183847686/section-2-the-basic-cold-climate-house
Clapboard attached directly to house framing could have been the original construction, but if you’re already doing an open-up-the-walls kind of renovation, I would remove it, re-sheath with exterior plywood and tvvek, and re-attach (as slopefarm suggests). You might have concerns about removal if it’s historic siding, but unless it’s seriously deteriorated, this shouldn’t pose a problem, and if it does, then you’re probably going to need to replace the siding anyway.
Under the siding on teh exterior wall, there should be a layer of exterior grade plywood. If Jim Hill is right, and you have clapoard attached to studs, it won’t hold properly. By plastic sheeting, do you mean Tyvek or similar substance? That should be on a plywood or similar substrate.
Assuming you have, from outside in, siding, tyvek, plywood, studs (between which the insulation goes) then interiro wall, you might be ok. As others have mentioned, it is better than overstuffing. If you have openings in this exterior wall, for wires, pipes, etc., make sure the insulation and weatherproofing isn’t compromised in these areas. You could have a perfectly sufficient wall and cold air blowing in through the outlets if this isn’t done right. Also, how close is this side wall to the next house? If it is a narrow alley, you won’t get much wind exposure, which will help a little.
I’m having a real hard time picturing what you’re describing. It sounds to me like you have (from the outside-in): siding (clapboard) nailed to studs, air space, plastic sheeting, R-11 insulation, then what – sheetrock on more studs? What is the R-11, rigid foam continuous across the studs?
I disagree with the above see no reason why you would not get some fiberglass or other similar insulation made for stud walls, and fill the 4″ air space with it. Yes, air space does create some insulation, but when it gets bigger than a fraction of an inch, a convection air current can develop, which will reduce the R-value of the assembly.
In this environment, in which we are either heating or cooling the interior environment almost 80% of the year, it makes sense to over-insulate. You’ll quickly make back the cost if installation in energy savings, especially as energy costs continue to increase.
Jim Hill, RA, LEED AP
Urban Pioneering Architecture
Between the wood, sheeting and R-11 you have more than enough insulation. The main determining factor in the end will be draftiness. You should be fine as long as the vapor barrier is finished well at the top, bottom and sides of the exposed wall.
sound like you are using fiberglass? if so, the higher the insulation R value, the thicker the insulation and more space required. It should not be “packed” at all. If you have the space for a higher R value then you should use it. but buying a higher R value and squishing it into a small space does no good. The vapor barrier prevents condensation. there are many “how to’s” provided on the internet. the seems should also be sealed.
air gap with vapor barrier and R-11 insulation is pretty standard for residential wall construction.
welcome to Brooklyn. I bought my house fully renovated
(poorly renovated) and it’s fully detatched. They didn’t put any insulation in. I had to open my walls and do it myself.
Dead air is a good insulator, that’s why attics were used before insulation and double layers of brick with air space. But today we have insulation so why not use it. It works by trapping air and creatindg dead air.
If you have the room and the walls are open why not. It’s not overly expensive.
In cold countries like Canada it’s against code to not insulate after you open up a wall.
Just don’t pack it too tight it’s counter productive