air sealing of ceiling joists

[KeirO]

Hello everyone. we are having some work done on the house and part of the ground floor ceiling has been taken down.

I am aware that there can be alot of eair leaks around the wooden ceiling joists (they pay through the inner leaf of the wall). But how is it best to go about making them airtight? expanding foam/celotex/mastic?

Any helps would be greatly appreciated

[rhys]

Check Green Building Store for suitable tapes and sealants. Best way if you have access all round. Ask them for advice as to the best product for rough wood surface and masonry.

[biff]

hello keiro,
               the air in question is coming out of the cavity and through the gaps between the joists and the beamfilling,,the traditional way to do this is to mix 3 of builders sand and 1 of cement,make it nice and fatty(pliable) and work the mix into the gaps taking care not to let it fall down into the cavity,
       the reason we use sand and cement is to keep out the mice and their cousins, i have seen bodgett and leggett use carlite browning and leave an airtight job,however the mice can tunnell through the browning quite easy,so sand and cement seems the best,expanding foam might just go straight into the cavity unless you blocked it with newspapers, etc, and the mice might like a chew on the foam.
                                                     biff

[gb484]

I'm not sure that this is what you need, but have a look at the 'Tony Tray' for air sealing of joists: http://www.tonyshouse.info/tony.htm
Even if it's not what you're looking for, this website is very informative and interesting. Many thanks to Tony!

[wookey]

I tried the GBS-recommended scheme of orconF on the joist with plastic sheet wrapped over and taped (pro-clima tescon) to internal airtightness layer and it was fiddly and ugly. I stopped doing that and started just using tescon alone, over an orconF bead to take up the sawn wood irregularity. This works but is still really fiddly to do - invest in the tescon profil tape which peels off in three parts, which helps, and make sure the wall you are taping to is flat - mine started off being inset (due to no plaster between joists, but there is above and below), and that was _extremely_ fiddly.

I have pics on the net somewhere: (here, in fact)
http://www.navitron.org.uk/forum/index.php/topic,11089.msg121478.html#msg121478

At Ecobuild I saw DAFA have a three-sided slot to make this a lot quicker:
http://www.dafa-as.com/products/dafa_airstop/rafter_shoe_collar
then you just tape the remaining side. I got a sample to try :-)

[biff]

this business of tape around the joists is most pecular,most pecular.
                       if you are working with a passivehause where everything is measured to the last mm,,fine,, but from what i see you are trying to seal the beamfilling between the joists,or what we bricklayers used to call the nosebleed,we used a 13 and a half cut mostly jointed on both side and fired it in,if times were good we could get away without flushing the joints in the beamfilling,if work was scarse we were made to seal the gaps a good as possible,
            flushing up with a good strong mix of mortar will allow the timber to breath and strengthen the wall as well as sealing the gaps.
                                                biff

[titan]

Joisthangers are the best solution but probably not possible as a retrofit with just the ceiling removed. Compriband 600 is used a lot on Oak framed houses for sealing joints etc www.tremco-illbruck.co.uk/products/00816_index.html

[rhys]

I tried the GBS-recommended scheme of orconF on the joist with plastic sheet wrapped over and taped (pro-clima tescon) to internal airtightness layer and it was fiddly and ugly. I stopped doing that and started just using tescon alone, over an orconF bead to take up the sawn wood irregularity. This works but is still really fiddly to do - invest in the tescon profil tape which peels off in three parts, which helps, and make sure the wall you are taping to is flat - mine started off being inset (due to no plaster between joists, but there is above and below), and that was _extremely_ fiddly.

I have pics on the net somewhere: (here, in fact)
http://www.navitron.org.uk/forum/index.php/topic,11089.msg121478.html#msg121478

At Ecobuild I saw DAFA have a three-sided slot to make this a lot quicker:
http://www.dafa-as.com/products/dafa_airstop/rafter_shoe_collar
then you just tape the remaining side. I got a sample to try :-)

Useful Link thanks - will the rafter shoe collar stick to blockwork  web link seems to show it with vapour barrier?

[wookey]

I haven't tested how sticky it is, but I wouldn't expect anything less than bituminous tape to really stick to blockwork. And it's fairly pointless sealing to blockwork anyway as that's not airtight - you need to cover it with plaster or a membrane.

[biff]

exactly wookey,
            sure thats what i have been saying, a good mix of 3 and 1,,nice and fatty and trowelled on with fervour should do the job.
                                                               biff

[wookey]

That'll seal blockwork, but not to timber for very long - timber moves. So yes, seal masonry with plaster, then seal joists to plaster as described above. (or using contega tape if you are doing it _before_plastering.

[rhys]

Plaster should really go over the tape not beneath just like a window tape seal.

Here is what looks like the correct material for smooth timber or membrane to masonry.
http://www.greenbuildingstore.co.uk/media/page_content/Airtightness/PDFs/Contega%20PV.pdf
The are three type of Contega, sealing timber to masonry, bedding in gypsum not sure if one will stick better to unplanned timber.