Spray foam for 115 year old building?
Howdy all-
I’m currently in the process of getting quotes from spray foam contractors to do the exterior walls and roof of my 115 year old rowhouse here in DC. The house is structural soft brick, double wythe construction with a small (maybe 1/2″) air gap between the layers. I’ve stripped all the plaster and masonry coating off the walls in the house (it was in terrible shape in most places) exposing the brick. My walls will be furred out (on the interior side) with 2″x4″s, and they’ve got 2″x8″s in the ceiling to fill.
I have had two open cell guys come and check out the house (Icynene and Biobased dealers) and neither seem to be concerned with the porosity of the brick or that their products are vapor retarders, not barriers and will absorb water if the vapor drive is high enough. Of course, they only had bad things to say about closed cell. The one closed cell guy I had come out (Corbond/Resintech) does mostly open cell, but agreed with me that in my application, closed cell would be the ticket.
All the quotes have come in at about the same price, so that won’t be huge factor in my decision. What I’m most worried about is the applicability of open celled foam for a building envelope built and designed 115 years ago when vapor intrusion wasn’t a major concern. The SOP in this area is to fur out the interior, put in faced batts and drywall over that (yup, no vb. I can send pictures of the rowhouse renovation down street from me… a $750,000 rowhouse by the end of it). In some places, I have seen them install a plastic vb under the drywall, but it’s not common, so I’m sure that regardless of what I do, it’ll be better than 99% of the crap work that gets done in this city.
I can understand the applicability of open celled foam on new or recent construction, but I can’t really understand why I wouldn’t do a closed celled foam if I know that the brick walls will breathe, and with DCs high humidity, will probably experience significant vapor drive during the cooling season. Not to mention that the brick will get wet and will need to dry somehow, and I imagine that I don’t want them to dry to the inside of the house. Closed cell, AFAICT, will practically prevent any moisture movement across the foam/brick interface, so will keep moisture from being absorbed into the insulation, and hence into the house. It will mean that the brick will take longer to dry, but as long as their not wet when it freezes it shouldn’t be a problem.
Are my concerns about open celled foam unfounded? Both open celled dealers touted the breathability of the foam, and that if I installed closed cell, I’d need an ERV/HRV. I didn’t mention that I was pretty sure even open celled didn’t breathe enough to not warrant some kind of air exchanger…
Thanks,
Z
Replies
Hmm, that's some tough sleddign by any stretch.
In the pendulum-swinging DC climate, you really want the insulation outside of the masonry mass (mostly). But, that's a non-starter.
That really just leaves insulating from the inside.
Now, to me, since it's already a porous sort of wall, as long as you know the 'direction' the moisture is traveling, then you have an idea on how to treat it. So, closed cell against the inside brick wall would not be outrageous, as the moisture ought (ought) to go to the sapce between the wythes and then down to the weep holes. Done. Ought is such a contrary word though.
"So, closed cell against the inside brick wall would not be outrageous, as the moisture ought (ought) to go to the sapce between the wythes and then down to the weep holes." Just to be sure, you really mean "closed cell" and not "open cell" in the above? I'm not even sure that the space between the wythes is clear in most places and I've not seen any weep holes ;) But I'm pretty sure that moisture will want to move into the house regardless when there is a 30-40% difference in RH between the house and the outside, now I just have to figure out how to make sure that it doesn't cause any problems.I figure closed cell against the wall will be many times better than the crap I see being done everywhere else in this town. It's got to be better than 4" of FG batts and no vb ;)Thanks,
Z
This is for me a VERY interesting question.
First, either open of closed cell foam is going to be about 100% better for you than any FG, batts or blown, so definitely stick with the foam.
Second, I can't imagine why the open celled guys felt any need to badmouth the closed cell other than defensive posturing. MOST of the time closed cell will outperform open cell foam but is often more expensive. Sometimes the decision comes down to which is more available in your area.
I use Corbond a LOT. It grants a higher density, higher R-rating, and higher resistance to moisture and its damages, AND is treated to make it unfriendly to insects that sometimes make their home in foam.
That said, I think there could be an argument made in favor of the open celled stuff in your case. If I were you I would want to present the question to joe at the building science forum.
You are in a moderate climate which means that moisture can be assumed to move both directions in your wall system. Open celled would allow interior moisture to enter the package but would also allow it to continue moving to the exterior to equalize things. but by the same token, if the exterior is less than ideal, water could penetrate as far as the open celled foam and work its way to the interior surface with negative effects. The closed cell would act as a VB and stop this movement. It would also prevent interior moisture from passing into the wall and becoming a problem.
Where I see a potential negative for the closed cell is IF the wythe spacing does not allow for proper drainage of moisture in the masonry, the foam would retain heat to the interior and possibly allow that moisture contained in the brick to freeze and cause damage to the masonry.
So much depends on the condition of the masonry now and whether you have observed much water penetration to the interior of the double-wythe wall. Without much sign of that, I would definitely go with the closed cell foam for the greater R-value and the VB
Good luck!
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Piffin-Thanks for the feedback! I'm glad to hear that the answer isn't simple or obvious even for the most experienced of you all out there, because I've certainly tried to do all the research possbile, and the answer wasn't clear to me either ;)Any link to the Building Science forum? I couldn't find it on their website.As for the other qualities of the foam, has anyone experienced any issues with the foam adhering to masonry? I have scraped off as much of the surface mortar as possible, but it'll be close to impossible to get it all off, so I'm hoping that won't affect the foam application. Also, the closed cell dealer quoted me on 2" in the wall cavities, and suggested doing a hybrid wall, using unfaced FG batts to fill the rest of the cavity. Is there any advantage to this?As for moisture levels in the brick, I'm not sure that what I'm doing will any worse than the typical house flip here in the city. Most houses here get a nice coating of paint, most likely whatever exterior paint is cheapest at Homey D, so effectively have a vb on the outside of the brick as well... I'll be stripping the paint next spring since it is beginning to blister and peel, and looking at a variety of vapor permeable coatings like lime washes/paints and mineral silcate paints (Keim). I can't find the permeability of mineral silcate paints, but lime paints have perm rating >350, whereas latex is 3-5 perms.I think the true problem is that I read too much. I wish I could just slap whatever is hanging around Homey D on to it, fill the place with FG batts and cagillion non-insulated recessed lights, put in a 2x oversize HVAC unit, slap the cheapest vinyl windows in, and call it a day. But I can't, I want to do it right :)Z
Can you put some type of sealer on the brick? Just thinking. You know for the freezing problem!
-Lou
The problem is that a sealer will seal the water in more t5han it will seal it out
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ponytl raised an excellent point on using tarpaper to create an isolations sheet and another drain plane behind the masonry.I didn't catch for sure whether your house brick exterior is painted or not, or if you plan to paint it.Painting is one of the worst things you can do with soft brick. Some brick are intended to be painted and others can be destroyed in only a couple of years by painting it in some conditions.what can happen if water is trapped in the bricks is that it freezes there and the expansion then fractures the brick, blowing the surface right off, but also making other penetrating fractures that destroy it over time, weakening the whole wall. Back in the day, a whitewash was used to colour and protect brick. It is primarily lime and will let moisture pass through it, and the lime will help the old mortar with self healing.
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there are alot of issue here you are missing...
one you have a very soft brick... the inside layer of brick most likely is less fired than the outside layer (only 2? I'd guess min of 3 on first floor)... and you have a lime mortar... this type structure should never be painted on the outside... these brick need to breath... the air gaps between the brick layers are your path for moisture to escape... the lime mortar is also self healing... notice that you have no expanion joints in your whole building... this is because with the hard brick (soft by todays standards) and your very soft mortar (about 250psi) everything moves and the mortar is almost like a gasket...
all this is not a big deal if you don't care if the building lives for another 100yrs and if you aren't going to own it for the next 20... but I believe you are causing future problems...
If you have true concerns for the building... i think I'd attach felt paper to the brick... then fir out/frame... then spray the foam... so as it sprays onto the felt and the studs.. and not to the brick...
I've seen old buildings where the masonary needed to be pointed and they chose to just spray the whole wall with foam think'n it's insulate and take care of the tuck pointing issues... didn't work... lots of trapped moisture and caused outer mortar to also fail...
what you think is substandard in the other buildings around you in MHO is a better choice...these old building have to breath they haven't lasted this long by being "all sealed up"
do some research
good luck
p
Ponytl-Thanks for the feedback, but I don't think I'm missing the issues. I know about lime-mortar, I know about soft brick and I know about moisture and vb. And I don't think what I'm proposing is any worse than the shoddy work I see being done on million dollar rowhouses here in the city.First, for moisture to move through a structure, you need to have a gradient, or drive. Putting builders felt against the brick then foaming over is only going to cause any moisture in the brick to condense against the felt inside the house. Spraying directly onto the brick prevents this (at least with closed cell foam) because it bonds directly to the face of the wall, and doesn't have any air gaps. The condensing interface then moves back into the brick, instead of being inside the house. So then once the interface is within the wall what to do? I would posit that hopefully your drainage space between the wythes keeps a majority of the wind driven rain from the inner wythe. The moisture that does make it through, is naturally going to be driven into the inner wythe of brick since those would be dryer to begin with. But as soon as the sun comes out, and assuming you've not painted the house with a vb paint, the outer bricks will begin to dry and the moisture gradient will reverse. This also doesn't account for the mass of the brick and their capability to hold water without causing harm to anything else. They will naturally absorb and release moisture, and in the old days, I'm sure they released a ton of moisture to the dry insides of the building. But being that the houses didn't tend to be very well sealed, and had a ton of air exchanges (thanks to the huge fireplaces), I very much doubt that the walls ever felt very wet. But if you think that the standard practice around here works better, then I have to disagree. The reason (and perhaps the only reason) I see it working is because with a vb paint on the outside of the building, and no vb (or poor vb) on the inside, you're forcing the interior of the building to absorb the stored moisture. I would assume in 5 or 10 years if you were to pull the drywall off the walls in many of these houses, you'll see mold on the back of it, as the moisture is driven into the drywall (a vb, if I understand correctly, once painted) and condenses on it, instead of being driven outside to dry. I haven't seen anyone anywhere suggest that the condensing interface should ever be inside the house, as all you'll get will be moisture problems. If you look at the current thinking on insulating, the major move has been to get the insulation as far away from the interior of the house, to move that condensing interface out to the envelope of the building, and control the moisture with vb, drainage planes, and good continuous sealing. And that is what I'm trying to do, albeit with a 1' thick brick wall, the mass and porosity of which make it a hard question to answer.Z
your plan might be the best answer... have'n been restoring old (100+yo buildings) for 30yrs... I always look at others who are doing the same and their ways of doing same... always interesting to see how each addresses issues the original builders never had to...
I have never seen good results where anyone ever tried to seal brick walls in this type structure... my current project has 24" walls at the base and ends with 12" at the parapet... good thing my plans call for leaving all the interior brick exposed... with tons of cleaning and tuck pointing and with the thickness of the walls and the air gaps I don't have a clue what the R value is... but the building always seems comfortable even in these 100degree days it's not killer... (with no A/C)
painting the exterior seems to be the worst and shortest lived thing you can do... I've never seen the paint last (and look good) for more than 5 yrs in the best case... many less than 1yr
I wish you well
p
Ponytl-I wish I had really thick walls to even out the temperature, but here in DC the humidity is the killer. Anyhow, I agree about the paint, but there are a couple of paints that are very permeable and have been used on historic brick. Keim mineral silcate paints and lime paints. The lime paints/washes have the highest permeability of all being that they are a sacrificial coating (hence the need to whitewash regularly). Unfortunately with our increased air pollution and acid rain, they very maintenance intensive these days. The Keim paints (Silacote is another manufacturer) look very interesting, they are inorganic and chemically bond to the brick. I might just got for the peeling brick look. It's cheap ;)Z
I'm still reading catch-up here. I see you know you need a permeable paint for this brick.but still keep in mind that with moving your condensation point out in the brick instead of in a drain plane behind the brick, you are also trapping water there where it can freeze.Maybe freezing is not that much of a problem in DC??? I have only spent a few weeks there so I don't recolllect.
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