The walls of my terrace house are made of two leaves of standard bricks and the cavity is no more than 30mm. Is there any way to install cavity insulation into such narrow gap? I just found out about the YBS Airtec (aluminium foil + bubble wrap) which promises the performance of a 50mm polystyrene (despite being only 5mm thick) As I am redoing the innner leaf I would be tempted to use the Airtec... Has anyone come across similar issues? Any suggestion?
Thanks
Alex
In article , Alex writes
If you are rebuilding the inner leaf, I would suggest celotex (or Kingspan) as it is available in a range of thicknesses and is regarded here as the best insulation material, much better than polystyrene or others. I believe that the claims of foiled bubblewrap brigade are to say the least optimistic.
OK, I have just found out about Celotex...it seems they do 25mm boards which should do the job. I guess, I would also need some extra insulation installed internally...what's the best way? If the aluminium (from the cavity) reflects heat back into the room another celotex installed internally would reflect this heat back into the cavity and so on... Ideally, I would rather avoid any extra insulation (and waste of space) and opt for using thermal blocks instead of bricks (for the inner leaf) but I am not really sure if it is possible considering that my property is a terrace house (end terrace...that probably would help a bit). The rows of bricks from my neighbour change into blocks into my property...any problem with it?
Any comments welcome,
Thanks Alex
Reflective properties of foil have no bearing on heatloss: Its there as a vapour barrier only.
When using it, use the proper al foil tape to seal each bit to studs.
25mm celotex is not very much - about equivalent to 50mm rockwool. Its just about allowable in combiantion with twin brick. Not as good as one would prefer,. but a lot better than nothing at all.Sealing up airgaps is CRUCIAL in windy weather.
I'd say that is a fine idea.
Not according to tests. See Actis. Do a Google a uni in Florida did tests that were very positive.
Thermal blocks with Celotex in the cavity.
In article , Alex writes
They also do 35mm but you may not be able to find a local stockist, worth searching around for tho. I did a quick google & found that Travis Perkins stock 12, 20, 25 & 55 in the cavity wall type so at worst you could add 20
Yes, it would be a real faff to add more & the thermal blocks sound like a good idea, but I am no expert in that area. Even if you had to build it in brick, I would guess that a cavity with 35mm of celotex would be better than a standard empty cavity or even one with rockwool batts. Maybe it's time to put some figures into a central heating type calculator to see if it will make that much difference, or do you have to satisfy a BCO that it meets a certain figure?
When I refer to my concerns about using blocks I am not focusing on the advantages in terms of insulation but about the possible drawbacks of mixing bricks (from my neighbour) with blocks (my property), i.e. is it structurally OK? Anyhow, the work on the inner leaf has to be done on two external walls purely for structural reasons (bulges and tie corrosion); therefore it seems appropriate to grab the opportunity for installing extra insulation. By the way...as I just discovered the thickness of the old bricks is a bit more than 110mm (these old bricks are very irregular and often and reach 120mm)...by using the blocks (100mm thick) I can gain some extra
20mm cavity space which should add to a total of about 50mm. Now really starts to make sense...Thanks for your comments Alex
New concrete blocks tend to shrink slighly whereas new clay bricks (ie. recently out of a kiln, so not the case here) tend to expand slightly. The effect is only really of significance over a storey height or more. Your bigger problem would be if lime mortar has been used in the original construction as there would be different structural responses to movement of the walls. In this case I can't see that there would be significant structural problems but I wouldn't be surprised if a non-structural crack forms at the interface. You may get reflective cracking through to the surface of the plaster unless you take steps (movement joint in plaster/building paper+EML etc).
On 5 Oct 2004 17:14:22 -0700, a particular chimpanzee named snipped-for-privacy@yahoo.co.uk (Alex) randomly hit the keyboard and produced:
Are you sure the cavity is meant to be 30mm? I notice further down in this thread you mention that the inner leaf is being rebuilt because of bowing. Cavities were normally 50mm, or none at all. It could be either that your inner or outer leaf has bowed inwards reducing the cavity, or it was meant to be a solid wall, and the headers have snapped (or non-existent, which I've seen happen). Either way, you should be looking to rebuild the wall plumb and maintain the original width.
Most cavity insulation requires a clear cavity. In sheltered locations Celotex or polystyrene requires at least a 25mm clear cavity, and in more exposed locations, the full 50mm should be maintained. There are some insulations such as Dritherm mineral fibre batts, which can be used to fully fill the cavity, but these don't come in anything less than 50mm thicknesses. I remain to be convinced about the effectiveness of foil-faced bubble wrap; nevertheless, from memory it requires at least 25mm clear space both sides in a cavity.
If for some strange reason your cavity is 30mm, I'd keep it clear and insulate on the inside.
Squirting poly foam in would do no harm, and is better than nothing.
convinced
You really seem to be so assured about your knowledge... Yes the cavity is meant to be about 30mm believe it or not and Dritherm mineral fibre batts types are available from 25mm up to 100mm (or more?). Of course the first idea was to install internal insulation but I've found out that it is possible to save space and install cavity insulation even in my old house.
DONT use expanding foam, it will bring the wall down. And depending on which wall it is, the rest of the house might follow.
Yes, people have made that mistake before :) Oh noo, not me thank god.
NT
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