We are doing a loft conversion to our bungalow. The cavity between the wall is narrower than would be required in a modern new build. Inside our cavity are metal ties that have accumulations of rubble - the builder has tried as far as possible to clean this rubble off but nowhere near 100% possible. We are worried that this will cause damp. We are not sure either, if we should fill the cavity (what material would be best (if any) or to put insulation material on the inside wall- the wall facing into the rooms. We are not too keen on this last idea as it will mean losing a further 2 inches of space in all the rooms. Has anyone had a problem like this?
I am not able to address your question about metal ties, since I don’t know their function or what “rubble” refers to. If they could possibly have a structural purpose, then it would be advisable to hire a structural engineer to inspect them and suggest a solution to maintain their function. If they’re in sound condition, this might be as simple as applying a corrosion-resistant paint.
The insulation question has fairly simple solutions: If the wall cavities are open (interior wall facing material removed) spray-applied insulation can be installed before new wall cladding. If wall materials are in place, blown-in cellulose insulation can be installed by a qualified insulation contractor. This is typically accomplished by drilling a 2" diameter hole through the interior wall material at the top & bottom of each stud bay (typically 16" apart) and mechanically pumping insulation to fill the void. The holes are then patched flush w/ the surrounding surface, which is easy in plaster or drywall, but could be complicated if there are other materials involved. It is also possible to drill holes on the outside and patch the exterior cladding material.
I build steamrooms and switched from kraft faced batt to foil faced polyiso because of condensate issues. we insulate w/poly then 6mil vizqueen, 1/2"durorock. Would it better to us XPS? Thanks for your input
I recently found out that the R-value of poyiso insulation varies with temperature. The published R-value is determined at 75 deg F (when you don’t need insulation), but drops to less than R-5 at 25 deg F and at 110 deg F (when you do need it). I’ve written to some polyiso mfrs for exact figures, but have not received any responses yet. In contrast, XPS and mineral wool insulations show little variation in R-value in cold or hot conditions.
Absolutely…to me this has been a huge part of my reevaluation of ISO. I still think it has it’s place, but the R-value benefits over the other insulations are minimal at best.
Dennis, if metal framing…yes. If wood framing, maybe.
So far this discussion has been about walls systems. Polyiso is fairly common for roof systems. Are other insulations being specified for roof systems because of the R-Value variance?
Polyiso is also subject to shrinkage after installation so that joints open up, which is why it should be installed in two layers. Mineral wool does not shrink, can be used full thickness, and has sufficient density that a roof cover board may not be needed. For economy you can specify one layer of polyiso on the structural deck [which would keep it closer to its optimum R-value] with a layer of mineral wool on the top.
The polyiso facer is effectively a vapor barrier, especially after taping/sealing all joints and penetrations - Does your wall design really want a vapor barrier on the cold side of the insulation?
Foil faces may be a vapor retarder, but there are other faces that may not be.
Or the warm side of the insulation for those of us south of I-10.
I’m with Wayne on this – I can’t imagine any good reason to use XPS for anything except maybe under slabs. It is never in my specs, and I think there is a better product than XPS in every condition you might use it – except under slabs.
the contractors here in California seem to like it, and every single submittal with it gets rejected.
as for roofs: polyiso all the way, and I don’t take substitutions for that, either. As to Louis’s comment: the published values for polyiso aged is now considered to be 6.2. EPS/XPS still comes in at 5. High density polyiso (sprayed in place) will come in at 7.3 because there are no panels, and no panel edges. I have found one supplier for high density polyiso who makes it in board form. With the energy requirements going ever upwards, that smaller R per inch starts to add up in roof insulation thickness.
I am starting to like sprayed polyurethane foam in some conditions, and I have a client who used spray foam roofing with great success.
There was one higher education owner in our area who liked the spray foam roofing. I thought this was a bit bizarre since students have a penchant for going where they aren’t supposed to and that the number of installers was very limited. After they discontinued their insistence on using it, I heard that the birds liked pecking at it, and they couldn’t keep up with the repairs.
I have seen older coated foam roofs that looked like lunar landscapes - littered with craters where the top coating was damaged (by rocks, birds, windborne debris, etc.) and then UV began eating away at the foam. Then the craters became a perfect catch basin for water. They are a maintenance nightmare. I never had a client who had one who asked to have another.
The Maricopa County Community College District here in Arizona (I believe the largest community college district in the U.S.) uses sprayed polyurethane foamed roofing exclusively for its low-slope roofing.
If properly maintained (i.e. recoated approximately every 10 years), then it will last a long time. There are a few companies that provide a cementitious coating over the foam that does not require recoating.
Now that this post has been resurrected, I have to comment on John B’s comment on 6/18/2012 (I think I was in grade school then ). Anyhow, I wanted to reprint a section of Tech Note 21 on cavity walls and air spaces:
“Cavity. The cavity or air space between wythes should be between 2 in. (50 mm) and 4 1/2 in. (114 mm). Air spaces less than 2 in. (50 mm) can not practically be kept free from mortar bridging. Air spaces greater than 4 1/2 in. (114 mm) do not allow the normally prescribed ties to properly transfer lateral loads. Air spaces different from these can be used, but care in design and construction would be required. If larger air spaces are used additional ties and/or thicker ties may be necessary. When rigid board insulation is placed in the air space, the clear distance from the back side of the brick to the exterior side of the insulation must be no less than 1 in. (25 mm). This allows the mason to lay the brick properly and for the wall to still function as a drainage wall. Mortar protrusions should not contact the insulation as this is a direct path for water. These air space requirements also allow for tolerances in construction.”
So with insulation in the cavity, a 1 in. air space is allowable, but having a larger air space provides more leeway if something isn’t right.
As for insulation products in a brick wall, I’ll leave that up for you guys.