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Dense packed cellulose in historic brick veneer

BostonTudor07 | Posted in General Questions on

Our house (outside of Boston) was built in 1928 and, despite several renovations over the years, still has the energy efficiency you might expect from a home built 90+ years ago. 

One significant energy upgrade we are considering is to add dense packed blown cellulose to the walls. 

Currently the wall assembly includes:  brick veneer —> [assume 1” air gap and tar paper?] —> solid wood sheathing —> ~3.5  inch wall cavities —> 1.5-2” cork panels inboard of the wall framing —>  plaster wall —> several layers of paint and in some places wall paper (not vinyl). 

From what I’ve read on this site, I think there are three main potential issues I need to consider with respect to adding cellulose to the cavities:

1)  vapor diffusion and, maybe more importantly, air ex filtration inside to outside, leading to condensation on the wood sheathing during the winter. I would describe the house overall as very leaky at present so am worried about warm moist air reaching the sheathing and condensing. I’ve read that cellulose when packed adequately is fairly effective in resisting air movement, but am not sure how accurate that is in practice or if there are potential bypass paths that air may find, leading to condensation and eventually rot in the walls. 

2). Inward solar vapor drive:  I don’t know for certain what, if anything, is between the brick veneer and the wood sheathing to stop vapor diffusion.  We’re in a relatively cool climate, have significant shading from trees, and have solid wood as opposed to fiberboard, so it’s far from a worst case scenario for generating condensed water on the interior surface of the walls, but nonetheless want to be sure we avoid any significant risks. 

3). Lastly, with the insulation installed, our brick exterior will no longer be as warmed by the interior heat as it has been for the first almost hundred years to date. As best I can tell the brick is in good shape currently, but still worry what might happen if it starts spending several months of the year cyclically freezing and thawing.  It sounds like this is a bigger concern for lower quality interior bricks used in full masonry walls (vs veneer) and for joists/beams embedded in masonry walls, but still would hate to negatively impact the historic brick facade. Not sure if a brick sealer (e.g. siloxane) would reduce the risk?

I would greatly appreciate any advice on which of these potential concerns are most applicable to this specific situation, if any are a major concern and I should reconsider doing the insulation, and if there is anything I should do to mitigate the potential risks. 


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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Boston Tudor.

    I do not think you have much to be concerned about when adding cellulose to these wall. Dense pack cellulose has some moisture buffering capacity as well as some air sealing potential, so if anything you'll be improving the vapor profile and air tightness of the wall, if only minimally. Your concerns about freeze/thaw cycles are legit in some structural brick walls (Insulating Old Brick Buildings), but I'm not sure that the issue is the same with a brick veneer wall. I tend to recommend people consult a local expert, which you could do as well, if you are unsure.

  2. Expert Member
    Akos | | #2

    Brick sealers are rarely if ever a good idea.

    Take a look around the neighbourhood, there is good chance that houses of similar age and brick have been insulated. If you don't see a lot of spalling on those, chances are your brick will be fine.

    The one item missing from your list is dealing with window/door flashing. These are non existent on older houses. This works fine with un-insulated framing but turns into a mess with insulation. You need to take care of that before any insulation work. Watch out for any wood sills, these tend to be a big source of water leaks in older houses.

    Make sure they get all the cavities when dense packing. Sometimes these older houses have a lot of random cut off bays especially around windows. You want to get all of those as there are bit air leaks around there.

    P.S. I've insulated a century old balloon frame brick vaneer with cellulose and it was a night and day in terms of comfort and energy use. Well worth the effort.

  3. woobagoobaa | | #3

    Might be useful, from NS Builders 1930 structural brick near Boston ...

    Somewhat different in that they are talking about a structural brick wall.

  4. BostonTudor07 | | #4

    Thanks all for the helpful input! The exterior window sills are all brick with some sort of flashing underneath (you see just a small edge of what looks like lead flashing beneath the bricks that make the sill) so hopefully that part is ok. But the other flashings around the windows and around the doors we’ll need to investigate a bit further. And that makes sense about watching out for gaps that don’t get insulated and could become a pathway for moist air to find the now cool wall. Thanks again for the help!

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