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Clarification needed on several topics...


CHoltje
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I apologize in advance for this messages' length, but there are several issues I need clarification on (I've read opposing views on each topic, and haven't been able to find reasonable resolutions). That said, on with the show.

About the house: Single story contemporary, built in the early 70's above a dirt crawlspace (about 3 1/2 - 4 feet from floor to 'ceiling'). The crawlspace floor has a vapor barrier, is mostly (80%-90%) under ground-level, and resides under the entire house.

The crawlspace is vented though foundation vents. Originally, I figured this a Bad Thing, and intended to cover these vents especially in the winter. This changed when I realized the furnace collects its combustion oxygen from this space. I'm considering changing this, but this is for a later discussion.

The ceilings are all cathedral-style: very little room for insulation. The small attic there is has R-19 foil-backed fiberglass batts along the walls and linving-space ceilings.

Ok..

1) Does it make sense to insulate (and how much to insulate) the crawlspace walls?

2) How much insulation should be on the 'ceiling' of the crawlspace (Zone 2/3 on the heating maps)? With the vapor barrier on the floor, does the ceiling also need a barrier? The insulation there now is paper-backed fiberglass -- which way should the paper be facing? Towards the living space, or towards the ground?

3) What are peoples recommendations for improving upon wall insulation?

a) We're planning to reside the house -- what benifits does the Tyvek wrap provide?

b) In the residing process, what are our options for adding insulation? Does the foam wallboard make the most sense? How well does the polyisocyanurate work in walls (is this an appropriate application of it?)?

4) Looking to the future, we're also thinking of improvements to the roof. My initial thought was to remove the shingles, and lay foam boards on the exisiting plywood, then installing a second "false roof" on top to fasten the shingles. Would this improve the envelope significantly to make it worth it?

I think that should do it for now.

Thanks for your thoughts!

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1) Does it make sense to insulate (and how much to insulate) the crawlspace walls?

Insulate the walls only if the venting is eliminated in which case the crawl will become semi conditioned space.

2) How much insulation should be on the 'ceiling' of the crawlspace (Zone 2/3 on the heating maps)? With the vapor barrier on the floor, does the ceiling also need a barrier? The insulation there now is paper-backed fiberglass -- which way should the paper be facing? Towards the living space, or towards the ground?

If the walls aren't insulated and the crawl remains vented the insulation should be placed with the vapor barrier toward the living space. I typically use pegboard to hold the insulation up

3) What are peoples recommendations for improving upon wall insulation?

unless there's no insulation at all in the wall cavity there's probably no value to adding unless you have the wall apart anyway. There's only so much that can be done in any given depth of wall.

a) We're planning to reside the house -- what benifits does the Tyvek wrap provide?

tyvek is an air barier and water barrier for the exterior. If the house is sheathed in plywood the issue of needing an air barrier becomes quite questionable. Plywood has a very low perm rate. As a water barrier under siding tyvek is reasonably effective, but felt remains my first choice.

b) In the residing process, what are our options for adding insulation? Does the foam wallboard make the most sense? How well does the polyisocyanurate work in walls (is this an appropriate application of it?)?

if the walls are empty, or can be, icynene or polyurethane foam are both excellent choices. Adding foam to the exterior does add R Value, but to get any appreciable value the foam would need to be a couple inches thick and that creates trim problems for windows and doors. Cellulose is cheap and almost as effective as anything for R value.

4) Looking to the future, we're also thinking of improvements to the roof. My initial thought was to remove the shingles, and lay foam boards on the exisiting plywood, then installing a second "false roof" on top to fasten the shingles. Would this improve the envelope significantly to make it worth it?

creating an air space by firring the second roof a couple inches above the original roof will create a "cold roof". That's quite desireable, especially since you have cathedral style ceilings and will prevent the original sheating from condensation probelms.

I think that should do it for now.

don't forget that everything that's italicized is from a friggin home inspector

Thanks for your thoughts!

"There are 11 types of people in the world -- those that understand ternary, those that don't, and those that think they do."

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Originally posted by CHoltje

1) Does it make sense to insulate (and how much to insulate) the crawlspace walls?

No, the floors are insulated. Besides, the vents are open to provide makeup air. It'd be a waste of money to insulate those walls when you're going to be sucking cold air into that crawl anyway.
2) How much insulation should be on the 'ceiling' of the crawlspace (Zone 2/3 on the heating maps)? With the vapor barrier on the floor, does the ceiling also need a barrier? The insulation there now is paper-backed fiberglass -- which way should the paper be facing? Towards the living space, or towards the ground?
Leave it alone. It's fine. The kraft paper has an asphalt emulsion on one side that retards diffusion through it to the crawl. Just make sure the paper is snug against the underside of the floor. You asked how much you should have, but you never said how much you've got. Around here (Puget Sound - mixed climate), we've typically got 6-1/4inch R19 batts. Your winters are colder than ours, so you could go thicker - provided you've got the joist depth to accommodate the added insulation - up to, say, 10 inches with unfaced batts. I wouldn't go thicker than that, because you'll get convective looping. Most of the heat in your home is lost through the walls and ceilings anyway.
3) What are peoples recommendations for improving upon wall insulation?

a) We're planning to reside the house -- what benifits does the Tyvek wrap provide?

b) In the residing process, what are our options for adding insulation? Does the foam wallboard make the most sense? How well does the polyisocyanurate work in walls (is this an appropriate application of it?)?

Housewrap is primarily designed to be an air barrier. Any product you use on the outside of that wall plane to improve its insulative characteristics will also be an air barrier, so you'll be throwing your money away on house wrap. Besides, if water gets behind wrap it can't get out again. You don't want to trap water in a wall clad with foam. Just ask anyone who ever had a barrier type E.I.F.S. system go bad.

Your question about foam wallboard vs. foamed-in-place polyicynene is confusing. You didn't say that you intend to strip out the interior walls and remove the existing insulation, so why would you even consider polyicynene? Go with a closed cell foam, cover it with felt, fur it out and apply your cladding in rainscreen fashion. The felt will allow diffusion to occur without trapping moisture and the rainscreen will prevent infiltration by wind-driven water.

4) Looking to the future, we're also thinking of improvements to the roof. My initial thought was to remove the shingles, and lay foam boards on the exisiting plywood, then installing a second "false roof" on top to fasten the shingles. Would this improve the envelope significantly to make it worth it?
Well, if the ceilings are cathedral ceilings with shallow rafter bays and you intend to apply a new roof anyway, that's one way to go. You can use vented nailbase sheathing - essentially grooved, closed-cell foam sheathing with a layer of OSB or plywood bonded to one face. Strip off the existing cover, apply the sheating with a ridge vent and a vented drip and then apply your cover. This allows air to circulate beneath the deck and meets manufacturers' requirements for a vented deck.

This is the wrong venue for these questions. Home inspectors aren't really supposed to prescribe detailed solutions. It's more appropriate for us, once we've spotted an issue, to explain why it is detrimental to a home, explain how it should have been and tell the client to get a professional to correct it, than it is to begin describing complete processes. Go to the forums at the Journal of Light Construction Online at http://www.jlconline.com and ask them again. You'll probably encounter some gruffness from one or two there about it being a place reserved for 'contractors only', but it is the Editor's policy (I know 'cuz I'm one of his moderators.) that non-contractors can visit there as well and should be treated politely, so you'll probably get plenty of helpful responses.

ONE TEAM - ONE FIGHT!!!

Mike

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"Housewrap is primarily designed to be an air barrier. Any product you use on the outside of that wall plane to improve its insulative characteristics will also be an air barrier, so you'll be throwing your money away on house wrap. Besides, if water gets behind wrap it can't get out again."

Down here housewrap is what is normally used by builders.When properly installed it seems to work.The problem is most of it is not properly installed.I just wanted to clarify the statement about moisture not being able to get out.This following is from the TYVEK website.

The unique, nonwoven-fiber structure of Tyvek® HomeWrap® resists air infiltration and water intrusion, yet is engineered to readily allow moisture vapor to diffuse through the sheet, helping prevent mold and mildew buildup and wood rot. The fibrous structure is engineered with microscopic pores that readily allow moisture vapor to evaporate but are so small that bulk water and air cannot penetrate. Siding, whether it’s vinyl, wood, stucco, brick, or composite, does not completely prevent air and water penetration. Tyvek® is designed as a secondary defense to help manage a home’s wall systems.

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Hi Danny,

I wasn't referring to vapor diffusion. I'm talking about actual water. Water vapor and water molecules are two different things. Think Gortex. A jacket of Gortex will readily allow water vapor to escape through the weave, but will not allow water to pass through. House wrap is designed with the same concept in mind.

When you apply siding you punch thousands of holes through house wrap. Any wind-driven water that gets behind the siding and drains down the face of the sheathing can, and often does, get behind the material. If it can't get out again, because the bottom of the wall has not been improperly detailed, it rots the wall. Thousands of builders all across the US are eating jobs that they did 5 or more years ago and many have lost confidence in wraps and are going back to felt. Add to that the studies of wraps, which are not backing up the wrap manufacturers, and you've got a huge mess in the trade right now.

My predecessor at JLC Online - Paul Fisette - has done several scientific studies of wraps vs. felt and has written a few papers on the subject. Bottom line, never install wrap thinking that it is going to function well as anything except an air barrier because it won't.

ONE TEAM - ONE FIGHT!!!

Mike

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Sure,

Go to my Building Science Forum over on JLCOnline.com and search the archives. You'll find a few hundred threads that deal with it. Also, do a search of the JLC archives for 'felt' and you should pull up an article written by Marton Holladay, Editor of Energy Design Update, around 2001 and an article written by Paul back around 1998 or 1999. You can also go to the UMass Amherst site, go to the Wood Technologies Dept. and then search through Fisette's writings.

OT - OF!!!

M.

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