Question

Is Airkrete a good insulator for an addition to a house that doesn't have an HVAC system? Would Fiberglass or SPF foam be better?

Asked by Ryan
Covesville, VA

We heat with radiant floors and there is no AC. The walls are 2x8 studs clad externally with plywood. Ideally an R value of 30 in the walls and 38 in the attic ceilings would be nice.

Answer

Elizabeth DiSalvo

Answered by Elizabeth DiSalvo

Norwalk, CT

Trillium Architects

September 19, 2011

Airkrete is a great alternative insulation. The first house we put it in has been working well for 9 years now.

  • It is a very good insulator and it is very clean (relatively.)
  • It will perform better than fiberglass and it does not have any of the chemical issues that foam does.

Foam insulation

Foam has off gassing issues both in production and in installation. And some say it affects the homeowners long after installation. I am not sure about that.

  • We put foam in a lot of houses because it has a great R value (closed cell foam) and it seems to off gas quickly (you don't smell it anymore after about a week).
  • But I have been thoughtful about it lately and have not spec'd it as much.
  • Plus closed cell foam is especially bad for the earth in its production.

Airkrete is a simple green product. I would recommend it. It is also significantly cheaper than foam. (Well it is in our area.)

Air exchange

BUT keep in mind -- no matter what insulation you use, if you super insulate you have to provide air exchange.

You do not have to have AC but you need to circulate the air and circulate in fresh air. (I encourage my clients against AC actually because if you have a really well insulated house and a few fans and you open and close the windows at the right time, you don't need AC in a moderate climate. Saves you a lot of money and saves the earth too.)

You can ventilate in many ways.

  • You can put in bathroom fans that run on a timer and change the air.
  • Or you can put in an ERV or HRV, or there are some passive air intake solutions.

You can ask a mechanical contractor to help you with sizing for the air exchange you will need.

So, bottom line Airkrete good! Just don't forget to ventilate for fresh air! Sounds like you will have a very well insulated house.

Good luck!

Elizabeth

 

For more information:

Read "Do you recommend bio-based soy foam insulation?" a Q&A answered by Andy Ault.

Tagged In: insulation

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