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rugby style 12-20-2010 11:18 AM

Insulating between joists with double brick wall.
I have a 1920s full double brick home, with joists extending directly into the brick. I'm redoing the ceilings in several rooms on the main floor. I've torn out the ceilings, exposing the joists and in turn the brickwork between the wall plaster and the subfloor above.

As expected, now that the ceiling it out, the draft is substantial.

I'm considering cutting stone wool insulation (Roxul R14/R22 or similar) and placing it vertically between each joist, butted up against the brick exterior wall, to cut down on the draft coming in across the upstairs floorboards - the intent being to warm up my 2nd floor floors, which currently have a bit of a breeze running under them.

Is this a bad idea? I've heard that old homes need to 'breathe', but I think that refers more to the space between the double brick wythes, so I think I should be ok.


stuart45 12-20-2010 01:37 PM

Does the wall have a 2 or 3 inch cavity between the wythes?
You may find it better to check the joints are fully filled, especially between the joist and brickwork.
Nowadays sealant is used as timber always moves away from the mortar joint allowing air in.
Modern houses are air tested and this is an area of air loss, unless joist hangers are used.
Is the cavity sealed at the eaves?

rugby style 12-20-2010 02:08 PM

That's a good tip, thanks. I'm working on the 1st floor right now so no access to the eaves, yet. What type of sealer is recommended for around the joists? Masonry-specific caulking?

stuart45 12-20-2010 02:25 PM

We use a multi purpose silicone sealant which can be used to seal between window frames and masonry.

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