My husband and I are bulding our last house, a small hybrid timber frame. We are going to have icynene insulation sprayed in. We will also have a metal roof and since we are in southwestern Idaho the roof will be absorbing a lot of heat. I need to ask your advice. The main part of the house will have sips panels as the roof. Off of the main section there will be two small wings that are conventionally framed. I need to know the best way to insulate the roofs on these sections. Would it be best to spray icynene in the roof joists, if so then is special ventilation required? The builder has said the cheapest way to insulate would be to lay fiber glass batting over the ceilings and then to run an exhaust fan in each section to deal with the heat buildup. In the summertime we can have a month of 100 degree and over days. I have lived in houses before where one can feel the heat pressing down from the ceiling. In your opinion, what is the best way to deal with this situation?
I would also like to know of your opinion and experience with tankless water heaters. Many thanks.
Replies
I'm fearless enough to offer an opinion -
easy way is to solid sheath the roof and spray the underside - and that will work -
maybe a better way would to be to solid sheath and spray underneath, then fur and strap on top so as to vent the metal roof - see page 60 of the current FHB issue - - this will require attention to details -
I do not like the FG/fan idea much - I feel like its performance will be noticably inferior to the rest of your home -
I look forward to others opinions -
Thank you for your reply. I don't much like the idea either. If we spray the roof joists does that require any special kind of insulation. Many thanks.
If we spray the roof joists does that require any special kind of insulation.
I'm not certain what you are asking here - Icynene can be sprayed on/over many surfaces -
it doesn't sound like your 'two small wings' will have cathedral ceilings - in this case you'll want the foam to be applied not only to the cavities between the rafters, but over and encasing the rafters also - there will be a premium for this application because of the increased square footage/amount of labor needed to do the job - the detailing at the top plate/ceiling joist area could be interesting - will you be spraying the walls also?
"there's enough for everyone"
You're both right, sort of.
When you say others houses had heat radiating out of the attic chances are the attic didn't have normal ventilation and/or good levels of insulation. Few houses in Boise have decent attic insulation because everyone has been doing the bare minimums.
The contractor is right that the lowest cost way to get insulation value is simply insulating and venting the attic. We're building in Boise and can say without hesitation that R-60 in the attic will solve most of your concerns.
Having said that, spray foam does eliminate the need to vent the attic space and seals the house better than fiberglass or celulose. A good way to go is spray a few inches to the underside of the roof framing creating semi-conditioned space in the attic that no longer requires ventilation. Then add r-50 on top of the ceiling framing.
If you want to use the attic space for any of your HVAC equipment it's more important to have a deep layer of insulation for sound deadening.
Make sure your contractor includes some form of whole house ventilation and effective bath and kitchen fans since SIPs and tight construction doesn't allow as much air loss and the interior can suffer from a variety of stale air problems.
Placing remote fans for the bath and kitchen in the attic space allows for very quite operation.
Best of luck!
Beer was created so carpenters wouldn't rule the world.
My metal roof is alot cooler than black asphalt shingles.
thanks Don -
most of my experience with spray foam has been with coolers and ag buildings - tho I did play a small part in a house addition where the HO insisted on using his HVAC/electrician (well justified, best man in the area) and the Mennonite GC arranged for the foam contractor to come on a saturday so as to beat the electrical and duct rough-in -
a royal pimp -
"there's enough for everyone"
so as to beat the electrical and duct rough-in
I'll bet they enjoyed that experience!
Beer was created so carpenters wouldn't rule the world.
Do not put only a few inches on the roof deck and R60 cells below. That does not make sense on many levels.First off is handeling any moisture entering (or not) the attic. Only a few inches of Icynene will not provide enough insulation to ensure the condensing surface (inside surf of foam) is greater than 45F to avoid condensation. This is per ICC code.
FYI, the conditioned attic space should have no VB on the ceiling below it.Also, add up the cost and you'll probably determine straight Icynene is pretty close in total cost going on the roofline. No VB, no very expensive IC lights, etc...My 2 cents. I'm an Icynene dealer in MA and also a Mechanical Engineer. I have no interest in your project besides offering what I feel is the best solution. Stu
add up the cost and you'll probably determine straight Icynene is pretty close in total cost going on the roofline.
The cost isn't even close! I sure wish you lived closer so our state could take advantage of your low costs.
As for a few inches of polyurethane (I'm not a fan of Icynene), that has been a common method in our region to create semi-conditioned space. If you'd like to re-write our building practices feel free--just bring those ultra-low foam costs with you!
:-)
Beer was created so carpenters wouldn't rule the world.