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What is the right amount of insulation for a house?

Ryan Gerbrandt Published: Feb. 11, 2019, 9:57 a.m.Last updated: Dec. 1, 2019, 8:01 a.m.

I'm looking to build a small single level passive solar orientated house with double walls or Larson truss (either would have dense pack cellulose) on a slab foundation with radiant in floor heat.  I saw a post with a chart showing code built, better insulated and super insulated.  The chart showed monthly payments (mortgage and untilities) and the better insulated home had monthly savings over the code built house while the super insulated house cost more per month due to the added up front building cost.  I'd like to aim for the better built house with instant payback but how do I determine how much insualtion to use?  EPS under slab and on side, dense pack cellulose in walls and loose pack cellulose in ceiling.  Thanks.

Responses (4)

Mike Reynolds
Mike Reynolds Feb. 19, 2019, 9:11 a.m. Reply

Happy to help! Manitoba winters don’t mess around but apparently you don’t either, that’s a pretty good envelope you’ve laid out. Passive heat collection on the south is a great idea, and limiting the north side windows is good, as long as you don’t end up feeling like you’re in a bunker. Your design sounds similar to our Edelweiss House, we did include a few small windows on the north just to have a bit of light in the bedroom and bathroom at the back.  

I don’t want to steer you away from energy modelling, but at a cursory glance here are some thoughts –

Your slab insulation sounds pretty good, I doubt you need to go much more than that though. 9 inches of EPS is about R36, that will serve you well. Make sure than when you’re getting the slab designed to insulate below the footing. We’re building another demo house right now that will have a solar-air heated floor built from a kit product that has continuous insulation underneath. There are times when insulation below the footings gets omitted, that would quickly become the weak spot in your home if you didn’t insulate them well.

Koltech have certified Passive House windows, not sure about the other company, but just make sure they build quality products and offer triple-pane and gas filled interiors. Ask either window manufacturer about options for low-e coatings (see links below); ours were done differently on the south than the north which meant the south ones lost a bit more heat at night but gained a whole lot more in the day.

And since you’re going with Cellulose keep in mind it is relatively cheap, so when it comes to the ceiling, I’d consider maybe beefing that up a bit. You’ll be up there anyway blowing it in, so a few more inches to bring that up to R70 or 80 is not a bad idea.

One last point in terms of durability - make sure the wall assembly is done with a proper air barrier and vapour control layer. If you do go for modelling then that company or person should be well-versed in building science.

Here are a few links that may help you make some selections, especially for choosing your windows and ventilation system. Good luck!

 

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Ryan Gerbrandt March 20, 2019, 5:46 p.m. Reply

Awesome, thanks!