Adding framing to basement walls that have framing with insulation and vapour barrier.

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Posted by: from Waterloo Region
8/16/2018 at 11:53:23 AM


We have had a company in to do our basement. Their proposed idea has us adding a layer of framing 2 inches away from the current wall that will result in adding 8 inches around all our exterior walls. The current concrete wall has framing with insulation to the floor and a vapour barrier on top. They said they didn't want to pierce the vapour barrier and install drywall on top. They said we needed to run duct work to the floor level (currently vents are on the ceiling) and add a 2 inch gap between the 2 walls. I have tried to search this but can't find proof that this is commonly done. I want to make sure this is good practice. Thanks.

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Date/Time8/16/2018 at 5:10:51 PM

Hi Joe,

Regarding the HVAC they are correct, for proper circulation you need to have hot air coming in at floor level with cold air return at ceiling level.

As far as the framing goes, it's not common, but not wrong. They're adding an air gap to allow for moisture evaporation if any forms (abates mould growth). However, I am curious why they aren't simply removing the existing rolled insulation/vapour barrier and adding 2" rigid foam insulation and then framing the wall as normal in front of that (insulated and vapour barriered) that would bring your basement to current insulation R-value code as per the Building Code.

Hope that helps,


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Date/Time8/16/2018 at 7:05:41 PM


Tim's comment was basically correct. We would remove the existing framing and insulation. Then glue R-10 ridged insulation to the concrete walls. Then seal all the edges with Tuck tape. Then frame new walls etc. And insulate in the new frames as well.

This way you end up with R-34 insulation.

Hope this helps.

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Date/Time8/17/2018 at 9:33:00 PM

I fail to understand the thought process behind your contractors proposal; you haven't said if they intend to insulate the new cavity. Energy Codes were recently introduced resulting in a requirement for greatly increased basement insulation; any renovation involving the outside walls should mean meeting the new Code, which is probably R-20, whereas your existing insulation would likely be R-12 if it's 2 x 4 framing.

You need to examine the existing work to begin: if the existing bottom plates are not pressure treated there should be 6 mil poly under them (preventing contact with concrete below grade); although not required it is permitted to have a dampproofing membrane on the inside of the foundation, this could be poly or bituminous coating but must terminate at grade level by Code, it is more energy efficient to have studs spaced at 19.2 or 24" o/c as opposed to 16" which is more common in older homes.

If the existing framing is OK I recommend adding 2 x 2's or 2 x 3's to the existing framing to allow for additional batt insulation; also removing the existing air/vapor barrier & placing it on the warm side of the wall as required by Code (never heard of someone being reluctant to pierce poly with drywall fasteners).

Good idea (but not necessary with a wall insulated basement) to have the heat brought to the bottom if practical, especially in bathrooms; also best to have returns at floor level to draw cool air off the floor.

I recommend getting two or three contractors to give you quotes; doing so would likely result in a different opinion on direction.

Ian Derksen; Safety Codes Officer - Building

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Date/Time8/18/2018 at 2:42:07 PM

If the idea is to create air circulation, supply vents at top one return vent at bottom across from the supply, a box around the duct is enough.

The polyurethane membrane over the insulation, should be in between the concrete wall and the insulation to prevent condensation, there is no need for a vapour barrier because it is under ground, There for only the first four feet of the wall need poly in theory because of the freeze line but a good practice is to cover whole wall.

To answer your question there is no problem if you screw the drywall over the poly every house in canada over the last 50 years is built that way.

Building a perimeter wall saves a contractor extra corners, and less drywall and plaster work.

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