AP Foil Faced on block wall

Reply

  #1  
Old 10-17-06, 08:26 AM
Member
Thread Starter
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,338
AP Foil Faced on block wall

An energy auditor recommended AP foil faced (polyisocyanurate) on my basement block walls to stop air infiltration. I am looking at 1" thickness due to availability and cost.

Auditor's recommendations:

1. Clean and prep block walls
2. Caulk gaps and apply sealer to all block
3. Glue polyiso to block walls
4. Seal seams with foil tape
5. Seal top edge and around windows with caulk

I looked at the Johns Manville info. For interior jobs they show fiberglass in stud bays and then polyiso on the room side of the stud bays with 1/2" gypsum directly over the polyiso. They do not specifically address installation on the interior of a block wall.

Also the auditor was not sure about code requirements for covering the polyiso. So I asked the building inspector who said it probably had to be covered due to flammability. According to the JM spec sheet, SBCCI applies here, Sec 317 (1998). Flame spread is 75 or less, smoke developed is 200 or less.

However I've seen basements in new developments (in Minnesota) where they had just the foil-faced board on the interior basement walls - no studwalls, no gypsum or any other covering.

The issue with covering is that I want to insulate now and some years later I want to finish the basement, so I want to avoid the expense & trouble of covering now.

Questions:

1. Is what the energy auditor suggests a good way to go?
2. Do I need to cover the polyiso at the time of insulation?
3. Should I put fiberglass in the stud bays before finishing with gypsum?
4. Can I finish with something other than gypsum, for example something that would not get waterlogged in case of flooding?
 
Sponsored Links
  #2  
Old 10-17-06, 08:57 AM
Join Date: Mar 2005
Location: USA
Posts: 6,126
AP Foil Faced on block wall

I seriously question of the wording in the "energy auditor's" recommendation.

If you had an air space behind the foam then there could be infiltration. Since it is bonded, there is no infiltration. In any case, the concept of applying the foam to the concrete block wall is sound.

If he actually means air infiltration, where is the air coming from? There is virtually no air infiltration through a concrete wall due to the permeablity level and the lack of a pressure differential.

I think he really is recommending insulation and isocyanurate is a very good insulator. The foil on it is actually there to prevent "off-gassing" that can reduce the insulating value. Isocyanurate is a superior insulator and is possibly 50% better than the typical rigid extruded foams commonly used. The system works very well on the typical leaky wood frame wall by preventing the real infiltration.

I would seal/caulk around all openings. The rim joist area at the top of the concrete wall should have any cracks sealed(foamed) and the area filled with fiberglass insulation.

The question of covering the insulation is covered by your local building code. What you saw in Minnesota may or may not have been according to code. The Republic of Wisconsin has had a history of unique code requirements, so definitely get a local reading on what to do.

You may not need or want any additional insulation beyond the isocyanurate on the walls. Since the soil is a great moderator of temperatures, the temperature differential between the inside and the soil may only be 10 to 15 degrees and not the 60 to 90 degres you have above grade in the winter. Remember, your floor is the same temperature as the lower portion of the wall. By insulating, you deprive yourself of the benefits of the soil moderation in the summer when you are air conditioning.

Good luck!!!

Dick
 
  #3  
Old 10-17-06, 09:56 AM
Member
Thread Starter
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,338
Originally Posted by Concretemasonry
I seriously question of the wording in the "energy auditor's" recommendation.

If you had an air space behind the foam then there could be infiltration. Since it is bonded, there is no infiltration. In any case, the concept of applying the foam to the concrete block wall is sound.

If he actually means air infiltration, where is the air coming from?

By insulating, you deprive yourself of the benefits of the soil moderation in the summer when you are air conditioning.

Good luck!!!

Dick
Thanks for the prompt response.

The auditor did a blower door test and used a smoke stick to show me where the air was coming thru minute gaps in the mortar, and chinks and cracks here and there. About the top three courses (>24") are above grade, with a brick exterior. So in that sense it's not basement. I imagine that air is finding its way in above grade outside and the blower door just drafted it out wherever there was a path.

He only does energy auditing and will not make referrals, so I don't doubt his motives.

I hadn't thought about the summer benefits of uninsulated basement walls! The basement is pretty cool in the summer but I attributed most of it to the leaky uninsulated ducts.

Should I just seal the lower, below-grade wall portions and then insulate & seal the above-grade portions with the polyiso?
 
  #4  
Old 10-17-06, 10:24 AM
Join Date: Mar 2005
Location: USA
Posts: 6,126
Sounds like a typical Milwaukee city home. Solid with a brick veneer.

Yes, the air can come in through any cracks, but not through the solid part of the concrete masonry units.

If you apply the isocyanurate, do it from the top to the bottom. My comments on the extra insulation were to point out that you can have too much. At times, there is a point of diminishing returns. there is no magic line on the inside of a basement that corresponds to the grade level outside since heat transmission is also lateralt and not just between the inside and outside.

After 5 months on the Gulf coast of looking at what happens(mold) to normal gypsum board/sheetrock, I would spend the extra for the supposedly "mold free" variety if I thought there was the possibility of flooding. Check you gutters, downspout extensions and the grading around your house before finishing the basement even if you are in the area with the sandy soil.

Dick
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes