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Old 04-06-2014, 07:45 PM   #1
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Floor Insulation for Raised Cottage


looking at insulating my cottage floor, its a pier/beam raised foundation, about 2' off the ground, no skirt, 2x6 joists, 16oc, no vapour barrier below the subfloor, very cold winters. So far Im thinking 1" rigid foil foam between the joists, foam sealed at the seams, then rolux batts, then pressure treated osb, and then maybe an non-insulated skirt around the perimeter?
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Old 04-07-2014, 06:14 AM   #2
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Pictures...?

Foam is going to be your friend here and sealing up the bands prior to the installation of the foam is going to be critical.

What does the floor above consist of?

If you are going with rigid foam and the labor associated with that, I think you might be well served to look at 2" foam here. The weather you see is certainly severe enough to warrant it.
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Old 04-07-2014, 08:14 AM   #3
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We spray foamed our floor, and I recommend it. 2" of foam, and we can walk around on the floor (once the place has warmed up) in wool socks when the otside temps are in the -20 C range. We are similar to you, and in Northwestern Ontario. The 2" rigid foam option is first runner up. Everyone I know who has put batts up under a cottage has just ended up with critter and insect condos.
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Old 04-07-2014, 07:03 PM   #4
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Originally Posted by ptarmigan61 View Post
We spray foamed our floor, and I recommend it. 2" of foam, and we can walk around on the floor (once the place has warmed up) in wool socks when the otside temps are in the -20 C range. We are similar to you, and in Northwestern Ontario. The 2" rigid foam option is first runner up. Everyone I know who has put batts up under a cottage has just ended up with critter and insect condos.
thanks for the tip on the batts, there is no spray foam within 2 hours of here so definitely will be rigid foam, 2" for sure if I pass on the roxul. Im thinking the osb would keep the critters out, seems to do the job on the walls.
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Old 04-07-2014, 07:26 PM   #5
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Your foam board in the joist cavity should be on the joist bottoms instead, use a faced product (imperative) as that stops the moisture drive so any flooring above works- wood, vinyl, etc. If you add OSB on sleepers in-line with the joists- creating a 3/4" air-space- this will further decouple the system from the cold earth covered with poly. Fig.7; http://www.buildingscience.com/docum...n-crawlspaces/

Leave the air gap above the fibrous insulation in cavity for warm toes above; http://www.buildingscience.com/docum...al-performance

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Old 04-07-2014, 09:31 PM   #6
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Thanks Gary, trying picture this, so u would have 3/4" air space then the 2" foil faced rigid foam, then osb planks in the joists with sleepers, to hold the foam in place? how would the floor be warmer though since the air space below the floor would be the same temperature as the air just above the floor?
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Old 04-08-2014, 08:39 AM   #7
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We couldn't get spray foam in either. We're water access and pretty remote. We used Tiger Foam and did it ourselves. The problem people have had that I have seen with batts and OSB is related to the difficulties of getting good air and mechanical seals around penetrations. Where joists lay on beams; where water and sewer pipes or wiring come through - all are entry points for ants and mice. In one case that springs to mind, the OSB and plywood looked well sealed and unpenetrated. Once it came down, there were voids from where the mice had moved material to nest, and the mess! Only reason he pulled it down is that he started to notice a cold spot in the bedroom and decided to have a look see. He went spray foam.
What Gary suggests sounds like the Cadillac approach. I just wanted to share my personal experience (a mouse can get through a gap the size of my little finger). I wouls also suggest that if you go that way you get really anal about sealing every little crack. By the way, I have seen mice and squirrels chew through OSB to get where they want to go especially to enlarge a hole.
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Old 04-08-2014, 03:58 PM   #8
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Tiger Foam will have to look into that. Will definitely avoid the batts, and just stick with rigid foam, or spray foam between the joists. Did you put rigid foam over the joists ends to stop thermal bridging? If I did this do you think there would be an issue with having an air space between the 2" of spray foam (or 2" rigid foam) and the end of joists where the rigid foam boards sit? Also did you put a knee wall around the perimeter or just leave it open?
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Old 04-10-2014, 03:03 PM   #9
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Look at the Fig. 7 in the first link, same as a rainscreen wall required in your codes. Cavity insulation (w. air space above for warm toes- per 2nd link), then FB ON the bottom of joists, then sleepers for the air space (decouple radiation w.foil), then plywood sheeting against critters and air sealing (first air barrier; http://www.buildingscience.com/docum...wall-approach/) tape fb/ply joints.

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Old 04-14-2014, 10:47 AM   #10
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In our case, and this might be applicable for the OP given that he is northern Ontario and the crawl space is open piers, the solution was similar to what is shown in Figure 8b, Figure 9, and photographs 6 and 7 in the first link. We have even greater space between ground and floor (about 34 inches at the rear and 86 inches at the front). With the open spaces between the posts or piers, airflow is significant compared to an enclosed but ventilated crawlspace. The problems are major when the space is enclosed. My grandparents place was done like the place in Photo 1 and 2. It had Lino floors, but it did OK until they hoarded in the crawlspace. It became a teardown when the floor rotted.
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Old 04-20-2014, 07:14 AM   #11
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I think this is the idea for clarity... foil faced foam under the joists, not between... OSB under if you must? But it's going to be hard to find the joists!



http://www.buildingscience.com/docum...n-crawlspaces/
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Old 04-20-2014, 08:08 AM   #12
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im by no means an insulation expert, but from the little ive read, I have a hard time not putting a VB up against the subfloor (the rigid foam/spray foam). Yes the foil faced foam acts as vb, but it cant be good allowing the moisture from the cottage to make its way this far into the wall before being retarded. I definitely wouldn't do this for a vertical wall. I have not found a more confusing diy topic than insulation and the use of foam, without question.

Last edited by wilyum; 04-20-2014 at 08:19 AM.
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Old 04-23-2014, 07:04 PM   #13
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Quote:
Originally Posted by wilyum View Post
im by no means an insulation expert, but from the little ive read, I have a hard time not putting a VB up against the subfloor (the rigid foam/spray foam). Yes the foil faced foam acts as vb, but it cant be good allowing the moisture from the cottage to make its way this far into the wall before being retarded. I definitely wouldn't do this for a vertical wall. I have not found a more confusing diy topic than insulation and the use of foam, without question.
Good point! That is normally the case, read pp.6; "Cold climates", then the rest; http://www.buildingscience.com/docum...apor-retarders

So the FB reduces the chance of condensation happening in the cavity because the bulk of R-value and vapor barrier is outboard of the cavity, pp. 8-14, same link. Now the cavity moisture (if there is any- notice the amount that diffuses compared to an air leak) control is by the HVAC system, especially if you ADA the drywall- in this case; floor. Plywood(0.75 perms) and OSB (2perms) plus any floor covering or wood sub-floor/wood flooring will reduce the moisture drive and the cavity temps will not force a drive, no reason for moisture to go/settle there. Hence the air-tight sealing of ff FB joints as link showed. FB on bottom of joists- HVAC controls the cavity RH, same as room; http://www2.dupont.com/Tyvek_Weather...20Bulletin.pdf

Same as Remote System; http://www.cchrc.org/remote-walls

Did that answer your concerns?

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Old 04-24-2014, 03:18 PM   #14
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[QUOTE=wilyum;1334377]Tiger Foam will have to look into that. Will definitely avoid the batts, and just stick with rigid foam, or spray foam between the joists. Did you put rigid foam over the joists ends to stop thermal bridging? If I did this do you think there would be an issue with having an air space between the 2" of spray foam (or 2" rigid foam) and the end of joists where the rigid foam boards sit? Also did you put a knee wall around the perimeter or just leave it open?[/QUOTE

We didn't put foam between the ends of the joists and the rim boards. I'm not too sure what you mean by creating an airspace, because - in the case of spray foam at least - you spray it in to fill any voids.

We left our underneath area open. We store the windsurfer and stuff under there, and the clearances range from 32" at the rear to about 6' at the front. That leads me to my final point: Our approach with the spray foam works because it is open. I think the point the others are making is that if you plan to create a closed in crawl space (even if ventilated), you will want to go with the batts and foam board approach to prevent moisture problems.
In our area (Northwestern Ontario cottage country), we seem to have a hell of a time keeping animals out of both crawl spaces and insulated joist bays. I have seen porcupines and rabbits gnaw on plywood and create nesting holes. I have seen mouse nests in spaces that seem perfectly sealed from the inside. That's why we went the way we did, and so far no problems. However, we get good breezes underneath all the time.
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Old 09-14-2016, 01:35 PM   #15
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Re: Floor Insulation for Raised Cottage


so a couple years later I finally got around to insulating under the floor. I was able to find some cheap used 4" polystyrene, cut to fit between the joists with spray foam at the seams. Question, with this kind of foam, should I still put a vapour barrier above the subfloor before the laminate floor? Would 4" polystyrene act as its own vapour barrier and be air tight? I don't want to double vapour barrier and trap moisture.
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