[nemo77]

Hi. We have recently bought a house that has crawlspace approximately 250 sqft, which sits below the family room. The rest of the house has a basement. there is an entry point between the crawlspace and the basement.

We live in Norhtern VA, so zone 4. Our family room is colder than the rest of the house, partially due to having no rooms above the family room and the crawlspace below.

I wanted to improve the coldness, by adding insulation above and below.

The crawlspace is vented and I have a question about the current insulation.

There are fiberglass batts in the floor above the crawlspace. There is rigid foam board on 2 of the outside walls. The other walls do not have any insulation; one wall shares a basement wall and the 4th wall is an inside wall. The floor is has the poly runs up and taped up over 12" on top of the foam boards and also on the concrete walls without the foam board.

Trying to do my research, it is either insulating the floor above or the walls.

My question is this: Is it ok to have the rigid foam boards on the 2 walls?

Also, would it be ok to add foil-faced foam board to the floor above, the foil facing towards the crawlspace, and leaving the current fiberglass batts. I am not sure if the current batts are paper-faced or not.....it might be unfaced.

Thanks!!

 

[nemo77]

Wanted to update the post with a pic and update that the fiberglass batts are unfaced.

 

[Windows on Wash]

Foam should be on the two outside walls and of sufficient thickness. Think of them as insulating as basement walls. Be sure to pull back the insulation and seal the ribbon boards/bandjoists as well.

http://buildingscience.com/documents/digests/bsd-103-understanding-basements?full_view=1

At that point, assuming proper insulation, sealed and insulated vents and a vapor barrier is complete and well sealed, you can circulate conditioned air into the space. I am guessing there is some duct work in there it just needs to be sufficiently opened up for supply and return side air.

If you go back to the vented route: http://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

 

[Bud9051]

Also, would it be ok to add foil-faced foam board to the floor above, the foil facing towards the crawlspace, and leaving the current fiberglass batts?

There are two approaches, insulate the crawlspace ceiling and ventilate the space below, which appears to be what you have. Or, close off the ventilation and insulate the walls and rim area as Windows said.

Windows explained the second option, insulating and closing off the crawlspace from the outside and adding some conditioned air. I prefer this option as it works for summer and winter. Warm summer air vented into a cool crawlspace means a moisture problem. With the insulated and air sealed exterior walls that space becomes easy to heat or cool (actually dehumidify). But with that space warm during the colder seasons, the floor above will also be warm.

Check local codes in regards to needing a thermal barrier over that rigid insulation.

Bud

 

[Windows on Wash]

+1

Be sure to check with local code enforcement on the applicability of leaving foam exposed in that area. Better safe than sorry.

http://www.greenbuildingadvisor.com...mal-barriers-and-ignition-barriers-spray-foam

 

[Colbyt]

Any vapor barrier (foil is) should always be on the warm (floor) side of the insulation.

 

[Bud9051]

Colbyt,
In both summer and winter the house should be dryer than the crawlspace, assuming air conditioning in summer. That means the moisture in the crawlspace will want to move up to that floor above. Placing the foil facing the CS will prevent it from reaching the subfloor which may be cooler with the ac running.

In winter and in winter, if the foil were up next to the subfloor then the floor joists and related framing would rise to the moisture level of the crawlspace.

I agree what you stated is the standard advice, but does the above explanation make sense?

@nemo, the only foil faced rigid insulation that is rated to be installed without an additional thermal barrier is Dow Thermax. Finding it is difficult in my area and the price a bit high, especially with the minimum order requirements I have. Orange box was where I could order it.

But, if you have sealed the floor and sealed the walls, there should be little need for floor insulation, rigid or batts. With adequate insulation it becomes very inexpensive to heat that space and essentially heat the floor above.

Bud

 

[Colbyt]

Colbyt,
In both summer and winter the house should be dryer than the crawlspace, assuming air conditioning in summer. That means the moisture in the crawlspace will want to move up to that floor above. Placing the foil facing the CS will prevent it from reaching the subfloor which may be cooler with the ac running.

In winter and in winter, if the foil were up next to the subfloor then the floor joists and related framing would rise to the moisture level of the crawlspace.

I agree what you stated is the standard advice, but does the above explanation make sense?

@nemo , the only foil faced rigid insulation that is rated to be installed without an additional thermal barrier is Dow Thermax. Finding it is difficult in my area and the price a bit high, especially with the minimum order requirements I have. Orange box was where I could order it.

But, if you have sealed the floor and sealed the walls, there should be little need for floor insulation, rigid or batts. With adequate insulation it becomes very inexpensive to heat that space and essentially heat the floor above.

Bud

It makes sense the way you reasoned it but I have to assume that some engineer somewhere tested extensively before the standards were developed.

Since I also need to do a small amount of this I may research it a bit more.

 

[Bud9051]

LOL, "but I have to assume that some engineer somewhere tested extensively before the standards were developed." there you have to be careful. Much of the guidance we receive has been reduced to its simplest form and although it works in many places it can fail miserably in others. Due Diligence is always required. And be careful searching as even some of the pros can get caught just following along.

I've seen some information on this and will see if i can find it.

Bud

Here is a related discussion about vapor barriers on a crawlspace ceiling.
http://www.greenbuildingadvisor.com.../keeping-crawlspace-vented-insulation-options

 

[Gary in WA]

You get slightly better energy savings by insulating the walls rather than floor in a closed crawl application close to your location; http://www.advancedenergy.org/portal/crawl_spaces/pdfs/Closed%20Crawl%20Spaces.pdf

Check with local AHJ as you may need to address radon first.

The foil faced FB; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Insulation gap; http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance

Gary
PS. Getting technical; http://www.advancedenergy.org/porta...sture Solution Becomes Efficiency Bonanza.pdf

 

[nemo77]

Thanks for all the information everybody!!

So bottom line, I won't add any foam to the ceiling of the crawlspace.

The foam board on the walls is only 0.5 thick. To meet firecode, I would probably have to remove the pink foam board.

If i go with the closed crawlspace option....i would have to install thermax foam board. Is it ok to leave the batts, or do i have to remove them?


There is duct work in there that leads to the family room above. How big of a hole do I have to cut in the ductwork?

Also, from what i remember, there has to be some kind of exit air for air exchange purposes. Do i need to do anything besides cut a hole in the ducts?

 

[Bud9051]

You can leave the batts and if you can find and go with the Thermax you can install it right over the 1/2" already there. Air seal and detail insulation in the rim joist above the foundation.

Once you insulate that space and seal it off from the outside, you can open it up as much as reasonably possible to the living space. Providing a small opening in a duct only connects that space to the conditioned space when the fan is running. An open doorway would be an example of combining the space with the inside. Remember, it needs to be part of the conditioned space 12 months of the year.

Bud

 

[nemo77]

Thanks Bud! So a couple more questions.

As you pointed out, thermax will be hard to get a hold of. So my plan is to just remove the boards(due to fire code) and insulate the rim joists and seal off the vents and leave the batts. I will also bring the poly up to 6 inches from the top of the walls. Would this plan be ok?

For sealing the vents, does it have to be certain thickness for the foam baord?

For the rim joists, does it have to be foil-faced or un-faced?

Also, this is is a pic of my laundry room, which shares a wall with the crawlspace(What if I just leave it open like this or cover it partially with some plywood, Would I still need a hole the duct work?):

You can leave the batts and if you can find and go with the Thermax you can install it right over the 1/2" already there. Air seal and detail insulation in the rim joist above the foundation.

Once you insulate that space and seal it off from the outside, you can open it up as much as reasonably possible to the living space. Providing a small opening in a duct only connects that space to the conditioned space when the fan is running. An open doorway would be an example of combining the space with the inside. Remember, it needs to be part of the conditioned space 12 months of the year.

Bud

 

[Bud9051]

You should still have some insulation on those exterior walls. Cool walls will pull the moisture out of warm air. I like the big opening and it would do well at keeping that space conditioned, if the walls are insulated.

Look at Roxul, it can be used in the rim joist area and cut to fit very easily, bread knife.

Since this isn't a large space, consider Dow 1" TUFF-R
http://www.homedepot.com/p/Super-TU...t-R-6-5-Insulating-Sheathing-268426/100322374

It has foil on both sides and the thicker side is rather heavy. Local code officials might accept it as is. But since it would be a full vapor barrier you could glue 1/2" drywall to the inside for the fire rating.

Still thinking. They also make a special paint that you could use to cover the existing 1/2" rigid. Intumescent paint, not cheap, but would avoid removing what is there. I'd rather see 1" or more of rigid, but your area isn't as cold as maine.

Bud

 

[nemo77]

Hi Bud. the Dow TUFF is also not avaialble in my area?

How about this product?

http://www.homedepot.com/p/Thermash...-Rigid-Foam-Insulation-Board-787264/100549260

 

[Bud9051]

Well, from their web site: http://www.rmax.com/files/2114/5401/7820/Crawl_Space_Application_Utilizing_Rmax_TSX-8500.pdf

They are showing it installed without an additional thermal barrier and they are claiming an excellent fire protection performance.

I like it, but only your local code authority can say for sure.

Bud

 

[nemo77]

Ok so as a final confirmation to everything:

1. Insulate the rim joists with Roxul or foam board(unfaced or foil faced?).

2. Only need foam board on the 2 outside walls, the foam board(thermax or rmax, will check with local authority) going up all the way up to 3 inch from the top of the wall, so that there is a termite inspection area.

3. Use a 10-20 mil Poly run up 12 in above ground.

4. Seal the vents with foam board.

5. Use some plywood to cover half of that opening between basement and crawlspace.

6. No holes needed in the ducts.


Thanks again!!

 

[Bud9051]

1. Insulate the rim joists with Roxul or foam board(unfaced or foil faced?). Either
6. No holes needed in the ducts. For now

Bud

 

[nemo77]

1. Insulate the rim joists with Roxul or foam board(unfaced or foil faced?). Either
6. No holes needed in the ducts. For now

Bud

Hey Bud, what do u mean for now? When would this change? Thanks!

 

[Bud9051]

Hopefully there will be enough natural air circulation, but if not or it stays too cool, then you might want to introduce some conditioned air.

Bud