Dense Pack Cellulose Wall insulation

Ian MacKay July 26, 2018, 2:48 p.m.

On this page of your site (www.ecohome.net/guides/2266/dense-packed-cellulose-insulation-wall-systems/) you show an exterior wall with 10" plate & sill and two rows of 2x4 studs. This looks fantastic, but the idea of vapour-permeable membranes on both sides makes me nervous in combination with cellulose. In Ottawa, temp can drop to -25 in winter and reach +30 or more with high humidity in summer. Lots of heat, lots of air conditioning. Are you absolutely sure that no vapour barrier is okay? How do I convince the building inspectors?

Responses (1)

Ecohome July 31, 2018, 3:25 p.m.

Hi Ian,

I can see how it doesn’t exactly look like a vapour barrier in the diagram as it is black, but it is one. What you see on the interior of that diagram is the netting that holds the cellulose in place while allowing air to escape during injection, followed by a poly vapour barrier, strapping and drywall. And to be clear, you absolutely need a vapour control layer of some kind on the warm side of the insulation to be compliant with Canadian Building Code. 

And worth a mention while we’re on the topic - there has been a pretty big innovation in the injected cellulose industry that makes the netting unnecessary at this point. There are new cellulose guns on the market that suck in air as they inject the cellulose, so there is no longer a massive storm of cellulose particles that need to be contained, and no longer a worry of blowing out the staples holding the membranes together. Instead, you can cut a hole in the poly to access the wall cavity for injection and just seal it up afterwards. 

If you’re going with cellulose we would suggest you look for a contractor that has the new gear, and if you haven’t already made decisions on contractors, you could also look into manufacturers of pre-fab walls. The price as well as the quality can often be be better than what can be acomplished on site. 

We will be putting up another demonstration house about 45 minutes out of Ottawa starting in a couple of weeks, the walls are also going to be dense-packed cellulose, but they are going to be delivered to the site pre-made. 
 

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