Hi, I just wanted to throw out my plan for insulation and see what flaws anyone can pick out.

We have a 110 year old solid brick (double wall) home which we are currently gutting. We obviously don't want to insulate on the outside of the brick so the natural choice is to cut into the interior square footage.

I have been trying to do my research on this forum and the building science website and my plan is to frame the interior with 2" x 2" deep boards (preferred) or with 2" x 1" deep boards while leaving an additional 2" gap between the existing brick and the new framing. Then we will insulate with a closed cell foam in the 2" gap. This will hopefully minimize the heat loss through wood touching brick as well as maximize the vapor barrier and surface area of foam.

Anyone see any issues that may arise? I feel like this would result in a more seamless vapor barrier which would be beneficial since the brick is very old and very water permeable.

Should I go deeper than 2"? I thought if I go any deeper I would use an alternative material to spray foam like XPS to help reduce costs. I would really like to make this house solidly insulated so that it will be able to last another 100 years.

One other note: the spray foam will be one of the last steps after replacing windows and caulking / sealing as much as possible and as of now I am planning on some electrical outlets on exterior walls. I could move quite a few of the electric outlets to the floor, but want to know how much of a disadvantage it would be to have them in the walls.

Thanks!

Also, the house is in central Kentucky so mostly heating degree days, but very cheap electricity (for now).

-- Marli

By "double wall" do you mean a cavity wall, with the external brick separated from the interior brick with an air-gap?

How are the joists supported by the brick?

Vapor barriers are 2- edged swords. Depending on how structural wood ties into the brick and whether it's a vented cavity-wall vs. a solid brick makes a difference on just how permeable or impermeable the wall needs to be to protect against moisture issues. In most setups it's more resilient to use a semi-permeable (to water VAPOR), but air-tight and waterproof (to LIQUID water) layer, not a true vapor barrier.

All brick is porous, and takes on moisture by wicking in rain/dew, and the reliability of the masonry-wood interfaces may be impaired if the wall isn't allowed to dry toward the interior. In a cavity wall with the cavity vented to the exterior (or into vented attic) at the top the exterior wythe takes the brunt of the moisture cycling and the interior wythes stay much drier. In solid walls liquid moisture wicks toward the interior, and vapor barriers on the interior would raise the average moisture in the brick, putting the wood at higher risk. If it is a cavity wall, be sure not to impede cavity venting in any of your renovations, maybe even enhance it with exterior vents cut into the vertical mortar under the eaves, and drill out weep holes on the vertical mortar on the bottom course to give it some convection to the exterior. Many of these features were commonly done in the initial builds, but often mortared over during re-pointing.

It's safer to use high-perm mid-density foam an keep it well over 1 perm, eg: 2" of Icynene MD-R-200 would be about 2-perms at 2" (R10) and 1.3 perms @ 3" (R15). If standard closed cell polyurethanes are used, limit it to 1" depth (~R6, and typically 0.8-1.2 perms depending on vendor) and fill out the R with a fiber-insulated studwall on the interior side. UN-faced rigid board EPS (bead board, not XPS) at 2-3" (R8-R12) with seams & edges sealed with foam would also be lower-risk. Under no circumstances should kraft-facers or any other type of interior vapor retarder be used on the interior side of the mini-studs/furring. Wintertime moisture drives from the interior are well-bounded in KY, even a 2-perm foam layer would slow interior vapor drives suffciently to protect the wood interfaces from excessive winter moisture accumulation, and would allow the brick to dry toward the air-conditioned interior from summer drives without putting the furring or paper facers on the wallboard at high risk, so long as only standard latex is used as the interior finish. (Avoid vinyl or foil wallpapers.)

Before foaming the inteior, have a mason inspect the inteior brick and decide wither or not an interior parge of an appropriate mortar would be in order. A sacrificial parge of lime mortar can sometimes add centuries to the anticipated lifespan of a brick structure, and the only opportunity for applying it is during full-gut restorations.

Cheap electricity in a moderate mixed-climate sounds like R410A refrigerant heat pumps would be the way to go on HVAC systems. If the heating/cooling loads are small enough ductless mini/multi-splits can be as efficient as geothermal (or better) when air-handler & pumping power, and duct-losses are factored in.

BTW: It's very difficult to get flat walls with 2x2s or milled 2x3s. Metal studs or furring, or finger-jointed 2x3s (turned sideways) will likely be more satisfactory than milled lumber. Putting all of the foam between the stud & brick is key to maximizing performance, and this is even more the case with metal studs/furring.

Thanks Dana!

I believe there is an air gap between the two brick walls, but I will double check at several points to make sure. I have not seen any weep holes, but there has been quite a bit of "fixing" on the outside and paint, but will try to look for those as well.

The joists are inset into the brick, there is even a small cavity around them. Would I want to make sure to NOT insulate in this cavity to help with drying? Moisture could still get into the wood and seep towards the vapor barrier side and cause problems perhaps?

Another thing -- the interior brick wall has several thin horizontal strips of wood inset into the brick layers to allow for tacking of the original furring strips. There are only about 3 rows per wall and they are only about 1/4" to 1/2" thick at most. I'm guessing these would most likely suffer if a closed cell foam is used? We don't need them or plan on reusing them so far, but I wouldn't want to cause rotting and I'm not sure if the strips go all the wall through the wall layer or not.

I am not too familiar with parging, would the primary goal to effectively re-point on the inside and help prevent any foam from entering the brick cavity to prevent bricks from cracking?

Thanks for the info on the studs, straight walls would be nice after all the work we're doing!

And thanks for your feedback, I really appreciate it since it's been tough to find info for solid brick homes.

I would use XPS. If you do use furring strips + spray foam, then I would use two layers, one vertical and one horizontal to minimize bridging.

Putting an inch of a generic closed cell foam around the interface to the wood would be protective, since it keeps moist interor air from reaching the cooler parts of the wood in winter and condensing. You can safely go up to 3" with the higher-perm Iycnene closed cell product. If you used rigid EPS and spot-sealed around those elements with a generic closed cell product (or a FrothPak or TigerFoam type of kit) that too would be fine. As long as you don't go much below one perm on the foam, the brick can still dry to the interior.

The cavity in a cavity wall is a primary factor in moisture protection- you absolutely NEVER want to blindly fill it with something. In some cases (and this is extremely local-climate dependent) you can get away with blowing rock wool or even loose EPS beads into cavities without much risk (this is commonly done in the UK these days, on some types of structures, but only after inspection by a qualified tech to determine the risk.) Both top and bottom venting improves the drying of the masonry considerably. If the brick has several layers of exterior paint, odds are that the paint layers are highly vapor retardent, and while liquid water can still seep into the brick via cracks & imperfections in the paint, the paint blocks it from leaving easily as water-vapor. By being able to dry into the cavity, the moisture content of the exterior wythe will be lower, but unless there is some air exchange to the relatively dry exterior air, the humidity of trapped air in the cavity can be high enough to transfer moisture to the interior wythes of brick. Sun shining on damp brick creates huge spikes of water-vapor release, but when the sun goes away and the brick cools condensation will form on both the interior & exterior walls of the cavity. But with a top & bottom vented cavity, when the brick is hot it also induces convection out the top vents, pulling cooler and drier exterior air into the bottom vents (weep holes)- moisture is actively solar-driven from the masonry, and it's average moisture content falls- a LOT!

The parge would protect the existing mortar from degrading over time from moisture flows by retaining the mineral content of the original mortar and letting the parge take the hit. Matching the mortar type to the original (particularly on re-pointing) is critical in old soft-brick buildings, since a high portland-cement mix can be too hard,and cause cracking. A sacrificial parge can eliminate the need for re-pointing for a VERY long time.

The old inset- furring can probably remain (particularly if it's a cavity wall and much drier)- it may be riskier to remove it than to simply insulate over it. You may want to make some exploratory drills to determine their depth though, and see if they are mechanically supporting the bricks above them.

Read this, and poke around the BSC site for other insights on retrofitting brick buildings:

http://www.buildingscience.com/documents/digests/bsd-114-interior-insulation-retrofits-of-load-bearing-masonry-walls-in-cold-climates

In particular, look at figure 7, and the notes about permeability of rigid or sprayed foam solutions, and the detailing around where the wooden beams are inset into the brick.

If going for an all spray-foam solution, 3" of MD-R-200 would not require thinning to 1" at the beam insets, since it would still be well above 1-perm @ 3", and the brick would be generally drier, winter & summer in a KY climate at the higher perm rating. At 3" it would also be ~ R15, which is about the same thermal performance as a tight 2x6 studwall with open cell foam or blown cellulose for cavity fill. (And 3" of that stuff is usually about the same installed cost as 2"/R12 of lower-perm closed cell goods.) Whatever spray foams you use, pay close attention to the permeance specs- it' makes a difference. Rigid EPS is a lot cheaper per unit R, but it would take 4" to hit similar thermal performance, but R15 of XPS (also 3") would be too vapor retardent and inadvisable.

jonr,

I plan on using only vertical furring strips and just placing them 2" from the brick attached to a top and bottom plate attached to the existing floor and ceiling joists. If they seem too flimsy I might put a small 2" block in the middle to anchor it to the brick wall, but I'd prefer to have a continuous gap with nothing attached inbetween.

Dana1,

Just to be clear, I can almost use any type of insulation so long as I maintain a greater than 1 perm permeability through the entire mass of insulation? I like the recommendation of the MD-R-200 and will try to find someone locally who installs that or something similar. We also have a train track about a half block from our house, will the MD-R-200 inhibit sound similar to a denser closed cell product, but better than open cell?

Also, I should note the "fixing" of the brick was not done by us, the previous owners had done some obvious patch jobs. If the walls are clearly double with a cavity I think I will go ahead and look into venting them, if and where appropriate.

Thanks so much for the advice!

Marli,
I would be very cautious about framing walls using 2x2's in lieu of 2x4 framing. Even with mid span blocking, your walls will be 'weak'. With just drywall you will have a problem maintaining a straight wall. Should you try to hang anyting heavier, (cabinets, etc), I would be worried about the walls' stabiliity.

Thanks Wes,

I originally thought I would do 2x4 and just frame out directly from the brick, but I think I would like at least a minimal continuous air gap for insulation fill inbetween. I suppose I could still leave a 1" gap and then start the framing, but this would add an additional 5" (well 4.5" really) of loss of floor space per wall and I'll have to think if we can sacrifice that much floor space as some of the rooms are already quite small.

I am also concerned about inadvertently trapping moisture and causing rot or mold, hence another reason for the continuous air gap.

Any other recommendations?

MD-R-200 while called "mid density", is still the same 2lbs per cubic foot density as 99% of the closed cell foams used in wall applications. (There are 3lb foams used in other applications that qualifiy as "high density".) I'd have to compare mechanical rigidity specs to guess about sound transmission, but seriously, this is a BRICK WALL. The air-sealing qualities will be a far bigger factor on sound transmission than the density or rigidity of any interior insulation.

Yes, if you stay above 1-perm the brick will be able dry to the interior sufficiently enough to be somewhat protective of the interior wood insets even if it isn't a cavity wall (and even more so if it IS a cavity wall.) The compromise solution is to keep it well above 1-perm at some clearance around the wood interfaces by reducing the thickness of the foam, which keeps the localized area of the masonry drier than the wall-average. Even going as high as 3 perms would probably be OK, but that's not do-able in closed cell spray foam. Higher density open cell foams such as 0.7lb Demilec is too vapor permeable if it's solid brick, and may lead to wintertime moisture accumulation issues at thicknesses less than 7-8". But if it's a cavity wall there may be open-cell options at reasonalble R if you can give up 5-6" of interior space. (The 0.7lb Demilec Agribalance product is ~5 perms & ~R22 @ 5", and would probably be OK for a cavity-wall.)

Google [ Icynene Kentucky ] yields several results, or you can use their dealer locator: http://www.icynene.com/dealer-locator/ Discuss the nature of your issues with any installer, and don't let them sell you on the higher-R value of their other 2lb foam (MD-C-200) which has a much lower perm rating, but would hit ~R13 @ 2". I've seen 1.5lb density closed cell foams advertized from some vendors, but haven't read the specs on any of them. There may be options there as well- lower density is generally higher-perm, within a foamed polymer family (most spray foams used in these apps are polyurethane based.)

Thanks Dana,

I've read that stopping air infiltration can do a lot to reduce sound transmission, and if we need more sound prevention we may just take additional measures in the bedrooms.

I will be sure to get the full specs on foams. I have asked for specs before, but never actually got them. It seems like a lot of vendors like to talk about it only as "open cell" or "closed cell" and that's it.

Thanks so much, I REALLY appreciate the advice,
-- Marli

Most vendors will have the specifications available online,eg:

http://www.icynene.com/assets/documents/pdfs/Products/ICYNENE-MD-R-200-Specification-Sheets-US.pdf

http://www.demilecusa.com/Repository/File/SEALECTION%20Agribalance%20Construction%20Specification%20-%203-11-08.pdf

http://www.specjm.com/files/pdf/BID-0110.pdf

http://nhfoam.com/download/COMFORTFOAM178-data.pdf

http://www.demilecusa.com/Repository/File/6%20SEALECTION%20500%20Construction%20Specification%20-%2002-25-08.pdf

http://www.icynene.com/assets/documents/pdfs/Products/MD-C-200/ICYNENE-MD-C-200-Product-Specs-US.pdf

The most commonly use test method is ASTM E 96, and the rating is only valid for the thickness & density specified. While not precisely linear, it's roughly linear with thickness- if you double the thickness, the vapor transmission is about half what it is at the test thickness. If you're using half the thickness, the permeance is roughly double.

There is quite a range in 2-lb foams- note that the BASF product is nearly 1 perm at 2" (and probably OK at thickness in your application), whereas Corbond is 0.6 perms at only 1.5", and would be below 0.5 perms at 2"- less than ideal. (The BASF product is slightly higher R too.) Icynene MD-C-200 is also a bit on the low-perm side, 0.9perms @ 1.5", which would be ~0.7 perms at 2", and under 0.5 perms @ 3", compared to 1.3 perms @ 3" of MD-R-200 (but lower R too.) At say R20 (4"), you'd still be at ~1 perm with the MD-C-200, but a very low ~0.3 perms with R20 Corbond (~3"). If you had to take a wild guess at brand-X closed cell foam, 1.2 perms @ 1" , or 0.6perms @ 2" is about the middle of the road. In your climate with a interior insulated masonry wall application 1-2 perms is a safer bet than <0.5 perms.

wow thanks for all these specs Dana!

Would you say it's OK to use a lower perm on the underside of our roof? It's a finished attic, and we will be redoing the entire roof, but would a lower perm on the roof trap too much moisture inside? I am okay with using a de / humidifier for the whole house anyways.

Sprayed directly on the underside of the roof deck the low-perm goods are preferred. If you have sufficient rafter depth to achieve your code or other R-value targets you could even go with 1-2" of closed cell on the roof deck and fill out the rest with cheaper goods such as cellulose or blown fiberglass "blown-in-blanket".

See tables 3 & 4 on p11:

http://www.buildingscience.com/documents/reports/rr-1001-moisture-safe-unvented-wood-roof-systems

The nearest analog to a KY climate in their simulations would probably be Kansas City, which has somewhat more severe winter moisture accumulation issues than non-mountaintop KY locations. But even Chicago (which is more rigorous yet) does just fine with as little as 1" of 1.2 perm @ 1" foam on the roof deck, with an interior fill of cheap fiber, and fares even better with 2" of cc. foam (~0.6 perms.) The high-perm closed cell Icynene would be just fine there too, as long as you put 3" (1.3 perms) or more in. Code min is probably R38, but for cathedralized roofs they probably allow R30. With low-perm closed cell foam R30 would be 5", and a pricey $5 per square foot. With the higher perm foam it would be 6" and probably a bit less, but 2" of low perm would be $2/foot and R12-R13, to which you'd have to add 5" of interior fiber at about a buck a foot, with a total depth of 7" (2x8 rafters).

If you're re-roofing the place, putting rigid foam on the exterior would be cheaper. Rigid EPS or polyisocyanurate ("iso") board runs on the order ~10 cents/R/square-foot. R19 iso is ~ 3" thick, R20 EPS is 5" thick, figure ~ $2/foot. With 2x6 rafters you could then meet code with cheap fiber or open-cell foam fill in 2x6 rafters, and no interior vapor retarder would be necessary. And due to the thermal break the exterior foam provides over the rafters it would measurably outperform code-min. If using shingle roofing you 'd have to apply a nail-base over the exterior foam through-screwed to the rafters, but if steel you could go with through-screwed purlins. With a shingled roof you'd get better longevity out of both the shingles & nailbase if you use 1x or 2x furring between the foam & nailbase (again, through-screwed to the rafters) and mount the nailbase on the furring to provide a ventilation channel. (Screen the soffit ends to keep the ventilation gap from becoming a home for critters. Standard ridge venting works to encourage convection through the gap too.) Atlas, Hunter, and other iso manufacturers sell panelized goods with the nailbase already applied to foam- it's pricier up front, but it can be a labor saver (and usually still cheaper than an all closed-cell spray foam solution.)

Are you sure that brick is 110 years old.... Stop experimenting the Museum is the best place for it....

Thanks Dana,
we are re-roofing and our rafters look to be only about 6 inches so exterior foam would be good. I would like to do a metal roof, but we may end up doing shingles if our budget is way too tight (hopefully not). Would the nail-base essentially be a second roof deck?


Chloe, the brick is at least 110 years old.

Posted By marli on 10 Jul 2011 07:21 PM
Thanks Dana,
we are re-roofing and our rafters look to be only about 6 inches so exterior foam would be good. I would like to do a metal roof, but we may end up doing shingles if our budget is way too tight (hopefully not). Would the nail-base essentially be a second roof deck?


Chloe, the brick is at least 110 years old.

Yes, the nailbase is essentially a second roof deck, but it's not a structural element- it's primary function is for fastening the roofing materials.

Nailbase iso panels are used under metal roofing all the time, eg:  http://www.hpanels.com/2009/pages/p...eld-NB.pdf

It's OK to stack nailbase panels over standard rigid as well, but the fasteners required for through-screwing get to be a bit awkward (and expensive) if you're putting down more than 5" of foam.  (But 5" of iso is ~ R30 by itself)   A combination of blown cellulose between the rafters (R20) and 3" of iso (R19- 3.5" with nailbase thickness included) would get you to code minimum.  If you can find a source for reclaimed rigid iso (InsulationDepot.com or similar), it's probably worth taking it up to at least R50 with deeper foam. See:

http://www.flickr.com/photos/hu...578116766/

There are multiple vendors, large & small, vented & unvented of these types of panel:

http://www.atlasroofing.com/tabbed....l=58&tab=9

http://www.isidelivers.com/drupal/files/u1/ISO_LIT.pdf

http://www.rmaxinc.com/downloads/DataSheets/mvnb.pdf

With any of them, pay close attention to the fastener spacing & type requirements.  A typical 4x8 takes 15 fasteners at better than 50 cents-per, (closer to a buck if going 6")  so be sure to budget for it.

Yes so that is why i am saying the museum is the best place for that brick....

Dana,

You have international readers!

I can read english easily, but writing it is much more difficult for me. Anyway, I'll give it a try, hoping it won't be a disaster... 

I read a lot (GBA, Building Science, expert papers, etc.) about retrofit insulation of old brick homes, but never found exactly what I was searching for. Until I discovered this site. The case of Marli seems to match mine perfectly.

My house is 90 years old. It is built with "double walls" (cavity walls), external brick separated from the interior brick with an air gap of one inch. The joists are imbedded into the brick. On the inside, plaster walls are supported by wood strips. Mortar has been repointed recently, but it needed very small repairs. The walls have a good drying potential, so the brick itself still looks pretty good. In fact, ALL the bricks surrounding the home are in perfect condition. 

The house has never been insulated. Because it is very leaky, I would like to make it more comfortable and energy efficient. Of course, I would insulate the house from the inside.

So what's the problem? Your advices to Marli seem to be perfect for me. 

Except for one thing : I live in Canada, in a small town between Montreal and Quebec City, where it gets pretty cold during the winter and sometimes very hot and humid in summer time. The home is heated during colder months and it gets very dry inside. I use an air conditioner during summer and the RH stands between 30 and 40%. Moisture is not a problem, and I suppose it explains why the house is stil in very good shape after almost a century.

Would you say that the instructions you gave to Marli still apply under my climate? Which means using appropriate foam insulation, making sure the assembly remains over 1 perm to allow the walls to "breathe" on both sides and prevent any possible condensation damage?
 
Or should I just do nothing, except sealing and caulking, since the house is doing pretty fine and insulation would put the brick at risk? To preserve a beautiful old house is important for sure, but, says my chilly girlfriend, living in it without being frozen four months a year should also be taken into account.  

I would have another question. I'm almost ashamed to ask, but let's see... As you know, in the old days they used paints with lead. Pulling down the plaster walls can therefore be harmful. Do you think I could build a new 2 x 4 stud wall one inch inside the old plaster wall, filling the gap and the cavity with dense pack cellulose and completing the assembly with gypsum boards? In that case, could the old plaster wall, if sealed well, serve as an air barrier? Would I need a vapour retarder, or could the new latex paint do the job? By doing so, I would take extra care of the air leakage where the wood floor beams lean on bearing masonry, reducing the insulation as shown in the Straube's paper you refer Marli to. Even if it wouldn't be as airtight as if I used foam insulating, would that be an acceptable compromise? Or just a foolish solution?

I know by doing so I would lose footage, but I have plenty of room. And with thicker walls, my big yellow cat would at last have enough space to sit at the windowsill...  

That's a lot of questions in a single message, I know. But I hope you will be able to find some time to give us an answer.

Thanks for your help, and also to Marli for raising the matter.  
 
Yves

Adding an inch or two of taped rigid foam, then 2x4 studs and gypsum/drywall makes sense to me. I'd use a "smart vapor barrier" under the drywall to stop air and moisture (even if you could get away with just paint).

Hi jonr,

I will consider the possibility of using rigid foam if I keep the plaster layer instead of pulling it down. 

As I wrote before, I would like to keep the existing plaster walls, but I'm not sure if it's a good idea. The pros : easier work, no lead on the site and no plastic glued forever to the brick (in case I would insulate with urethane). The con : air seeping through the brick, passing round the new insulation and finding its way inside.

Just to make sure... Would you still put insulation (Roxul, for example) between the studs? It sure rises the "R" value, but I'm afraid too much insulation could put the old brick at risk. But maybe I care too much, since the parapet has never been insulated and the brick never suffered. So I guess colder (better insulated) exterior walls would also do fine over time.   

The "smart vapor barrier" looks like a very good idea. I just read about "MemBrain", I'll continue my research on that topic.

Thanks a lot, I truly appreciate your help.

Yves