Insulating under my house on Long Island

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Old 03-15-13, 01:44 AM
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Insulating under my house on Long Island

Separated from Basement Insulation Help

So after reading a bunch of that and knowing I need to re-read and try to figure it out, what are the suggestions? I live on Long Island in NY zone 4. Basement is 20'x25' with drop ceiling panels and wood framing (2x3) right against the concrete walls of basement. The walls have thin wood paneling nailed to 2x3's and no insulation. My rim joist has many air leaks but no contractors will do that small of a job for spray foam.There is about 2' exposed foundation on North and east walls. The south and west walls have concrete slab (15' distance) that is floor of living room on south and floor of family room on west.

10' of north wall has a 2' overhang / cantalever with big gaps on where thin masonite is attached to joists. The 3" thick FG insulation in these cavities is black as it's just an air filter at this point. The ceramic tile floor in kitchen that is above this overhang as you can guess is ice cold.

My plan is to drop the masonite, cut some small ridgid board for the end of cavities and can spray foam in place against the rim outer joist. Then I was going to silicone some 2" ridgid board against those joists and cover with new painted plywood. On the inside I was going to put some Roxul into those cavities.

ON the walls of basement I was going to either move wall out by 1.5" or add wood to inside so I have room for the Roxul while leaving a 1/2" air gap between concrete and insulation. Some of this reading says don't do that!

My friend bought a house with finished basement and they had FG right against concrete wall and drywall ceilings. Not sure if there was a vapor barrier anywhere else. 2 years after moving in half his ceiling collapsed in basement and everything was black mold. After big $$ for company to do mold remediation they just finished rebuilding the basement. The contractor did NOT use ridgid board against walls and made a big point of explaining WHY he left a 1/2" gap between the concrete and new FG insulation so that it would not get wet and any moisture could travel up as needed. He now has a dropped panel ceiling also.

I obviously don't want a mold issue. If the moisture can travel in that space won't the cold from the walls also travel up to floor above (or heat down) making that floor area cold? I'd like to reuse my studded walls that I have now and re-install the paneling. My plan was to just do the 2 exposed walls (north and east) with the insulation how much benefit might I gain by doing the other 2 that have 15' of conditioned space above the slabs. There is no draft issues on those to rim joists just on the outer walls.

Besides spray foam since 3 foam contractors said 50 board feet is not worth their time/my money, what is teh next best way to insulate the rest of the rim joist? Make an "L" with ridgid board and foam cans?

On the south east corner of basement is a 6'x6' area that is where my Boiler is so no studs on concrete walls.
 

Last edited by Nashkat1; 03-15-13 at 07:40 PM. Reason: To separate from earlier thread.
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  #2  
Old 03-15-13, 09:55 PM
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You've got a lot to consider. After a quick skim, let me ask you about two things, one of which you mentioned and one that you didn't.

You described the overhang or cantilever and your thoughts on improving that area. But unless I missed it, I didn't see that you were working with it as part of the conditioned space inside your house. It is, and here's a thought: What if, after you open and clean out that area, you install a couple of inches of XPS against the rim joists of the cantilever, stopping it 2" or so above the bottom of the joists? And then installed 2" or so of XPS across the bottom of each joist cavity? So you would have made a box with three sides and a bottom, but nothing on top and nothing on the side against the house. And then re-cover the bottom of the cantilever with new Masonite of plywood or whatever you like, and air seal that face? Or cover it with housewrap and don't air seal the exterior covering? But dress it, if you will, like any other interior/exterior barrier.'
'
The thing you didn't mention is the insulation and ventilation in your attic, and how well sealed the ceiling below the attic is. Getting that area in good shape, if it hasn't already been done, is likely to repay you in both energy savings and comfort faster than improving the basement insulation will.

Just a thought.
 
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Old 03-16-13, 02:01 AM
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Nashkat1,
Thanks for reply and questions. Actually third paragraph was just that idea. I have 3-4 inches of siding overhang on the outside of cantalever. the 2" of ridgid XPS will be 2'W x 10' long airsealed/glued/silconed to bottom of joists and then low expansion foamed (so I don't push fiber shingles off). The Roxul will help fill and add while leaving some space on top for air from basement. I plan to count it as part conditioned space. I hope to put some radiant stapled up with plates at least up to that area and maybe slightly into it.

When I box that out and add Roxul do I bridge over the 1/2" gap against concrete walls (if I do that)?

Attic has extra R-30 rolled out on top of original but also part of "on the list" projects to get up there and air seal openings at wires/plumbing etc, add ridge vent, Bathroom exhausts (out gable side/maybe soffit).

I want to get a efficiency test done with thermal at some point and maybe add blown cellulose to walls and/or attic.

Previous owner was busy using funds to support his other "interests " instead of looking to invest in the house and make it more efficient for his family. Other significant others can be expensive you know......

Basement windows (3) and 10+ double hings also on list. The current ones from 70-80's (vinyl replacements) the sashes are separating, seal between glass is gone.
 
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Old 03-16-13, 07:31 AM
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Under the overhang, I would not add any insulation under the joists, only in the joist cavities. Anything underneath will on be protected by and air-sealed against the overhanging shingles, which is probably not the best long-term setup. I would install 2" of XPS against the three joists that have an outside face and stop it 2" above the bottom of the joists, as I said earlier, then install 2" of XPS inside each joist cavity, at the bottom. No Roxul and no radiant barrier (no use there). A moisture-permeable air barrier, yes. Then the new covering - the plywood or whatever you choose. This under a floor, after all, and the money you save here can be better spent on the attic ventilation, the windows, or re-framing and insulating the basement. Leave the air flow between the overhang and the basement open.

The bathroom vents need to exhaust through the roof, not the gable ends nor the soffit.

Add the ridge vent and close all other exhaust vents in the attic. Add continuous soffit venting if you don't have it.

To get a handle on how much insulation would be optimal in each part of your house, you can enter your specific information in the ZIP-Code Insulation Program or a similar calculator.
 
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Old 03-17-13, 12:17 PM
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Good point on the siding. I was kind of looking at from the foundation side where my sill plate has many gaps etc. Going down would give me something to expand a foam against to help seal that. The overhang is on north west corner and the wind blows right under it. That floor area is like ICE all winter (right by kitchen table) so I wanted max insulation from the cold. I will definitely do the 2" XPS on the outside portion of those joists. Not sure if I mentioned but plans are to hopefully put some radiant loops under kitchen and they would go into those bays some. I figure at that point I need the extra roxul anyway.

What effect does the snow have on the roof vented version? This year we had a 30 inch blizzard and I didn't see the vent from my downstairs bathroom for about 1 month. Also all the things I read say to try and pitch insulated ducting out to vent not up to roof so condensation doesn't run back inside when it happens. We had many single digit days so there will definitely be some condensation insulated or not. I'm looking at getting the remote fan with possibly motorized sealing regulators that I linked in a different thread.
 
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Old 03-17-13, 10:33 PM
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Not sure if I mentioned but plans are to hopefully put some radiant loops under kitchen and they would go into those bays some. I figure at that point I need the extra roxul anyway.
To install the radiant heating under the overhang you will need to have the space open. What I would do this year, then, is air-seal the outer three joists with caulking, use the ZIP-Code calculator to figure an R-value for that space, translate that to Roxul, and install that at the bottom of the bays. 2" XPS can go against the outer three joists above that. Probably wrap a moisture barrier over the top of each piece of Roxul. Staple a housewrap to the bottom of the joists there and screw a new piece of plywood up to protect everything. I would be a bit picky with fitting the plywood but I wouldn't air-seal it. That way it can all come down if you want to add the loops later. Or it can stay that way forever, if you're happy with the result.

The attic, the windows, and the basement framing and insulation can all come before deciding on the radiant heating.

What effect does the snow have on the roof vented version?
IDK, to be honest. Others may. An interesting question.

Also all the things I read say to try and pitch insulated ducting out to vent not up to roof so condensation doesn't run back inside when it happens. We had many single digit days so there will definitely be some condensation insulated or not. I'm looking at getting the remote fan with possibly motorized sealing regulators that I linked in a different thread.
We don't know where that thread is, so could you post the link here also? The venting question has got me wondering now...
 
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Old 03-17-13, 11:38 PM
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Nashkat,
This was one of the threads http://www.doityourself.com/forum/du...st-piping.html

I'm not sure if it was all here at doityourself or combo internet search. My downstairs bath fan runs 4ft through joist then into attic area. Of course it turns up to get out of joist then across. Not sure why if they were cutting through roof anyway but they ran 6 feet over then up through roof to hooded vent. Ducting is not insulated currently.

I covered some of info here. http://www.doityourself.com/forum/du...heat-loss.html
 
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Old 03-18-13, 06:09 AM
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Hi sequoia,
If gables are within reach, I prefer exiting horizontally as you suggest, condensation can be a problem. Plus, extra holes in the roof can add future problems. But when you cannot exit out a gable, avoid the soffits when possible and go out the roof. Warm moist air ends up getting pushed back into the attic through the soffit vents.

I don't have the numbers at hand, others may jump in, but every 90 turn adds something like 10' to your total run and bath fans have a total length limitation. As for the tinker toy dampers these mfg use, installing something that works well would be nice. I read your other thread on the motorized damper and cheap rarely satisfies me and quality usually makes me happy. The incoming cold air is a tiny cost factor, since cold air is leaking in all the time, but it is a large comfort factor to not have it leak into your bathroom.

Careful with any insulated flex ducts, they collect water.

Bud
 
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Old 03-18-13, 03:41 PM
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I think Bud has given you the best answer on venting your exhaust fan(s). If you can't get to a gable end, it sounds like you already have an example of the preferred solution:
they ran 6 feet over then up through roof to hooded vent.
 
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