external insulation, window sills, do you need them?

timmer3

hi. i'm getting external insulation (EPS) done to a terraced pebble-dashed house. i got the end wall done a few months ago, and now that the SEI grant has come through i can use that to insulate the front and back of the house. the insulation thickness is 120mm, and this will be enough to completely cover the existing concrete sills, which only protrude about 40mm. my question is do i need window sills at all? i can get the installer to cut a slant in the EPS board to sit on top of the existing sill, to allow the rain to run off. but do i need any overhang? the silicate finish is dirt resistant. i've read about aluminium sills but some say they don't look good, and it seems difficult to remove the cold bridge. i like the thought of insulating all the exposed concrete. i'll be moving the doors and windows out to the edge to help eliminate the cold bridge.
thanks for any comments.

sinnerboy

Avoid lack of continuity in all insulations

Where the insulation level drops so does the thermal resistance and you risk localised condensation .

Cut the cills away flush with the wall and do not notch the insulation .

Do as you intend - i.e. move the windows out so that they are in the insulation zone . I would advise aluminium or pvc cills to improve weather resistance

timmer3

thanks for the tips sinnerboy, that's an excellent idea to crop the existing concrete cills. i'll look into the aluminium cills. cheers.

PCPL

I agree with the idea of cutting back the existing cills, they are a major area of heatloss, aluminium cills are the way to go, they can be powercoated any colour and are very easy to maintain

unitjk

PCPL wrote: »

I agree with the idea of cutting back the existing cills, they are a major area of heatloss, aluminium cills are the way to go, they can be powercoated any colour and are very easy to maintain

There is a product which is made of concrete that fits over the existing cill called the concrete overcill .

soldsold

unitjk wrote: »

There is a product which is made of concrete that fits over the existing cill called the concrete overcill .

Im all for doing the job right, but that sounds like overkill

:P

sydthebeat

unitjk wrote: »

There is a product which is made of concrete that fits over the existing cill called the concrete overcill .

the advantage of a pvc or aluminium cill is that the form is only millimetres thick... .

how thick is this 'overcill' product?

how is it supported? or fixed to the existing cill?

PCPL

sydthebeat wrote: »

the advantage of a pvc or aluminium cill is that the form is only millimetres thick... .

how thick is this 'overcill' product?

how is it supported? or fixed to the existing cill?

I have seen such a product, its basically the same profile as a regular cill with a huge rebate taken out of the back of it leaving a 25mm thick piece which is then stuck on top of the existing cill, it looks just like a normal cill but its made from a lightweight concrete material, i just had a small sample and found it quite heavey, wouldnt like to be lugging a 2 meter lenght up a ladder!! I would imagine they are quite brittle and great care would have to be taken while transporting them, they look a nice job but have yet to have NSAI certification so have to stick with the aluminium for any grant aided retrofitts.

unitjk

PCPL wrote: »

I have seen such a product, its basically the same profile as a regular cill with a huge rebate taken out of the back of it leaving a 25mm thick piece which is then stuck on top of the existing cill, it looks just like a normal cill but its made from a lightweight concrete material, i just had a small sample and found it quite heavey, wouldnt like to be lugging a 2 meter lenght up a ladder!! I would imagine they are quite brittle and great care would have to be taken while transporting them, they look a nice job but have yet to have NSAI certification so have to stick with the aluminium for any grant aided retrofitts.

As far as i know they are part of an approved system which i cannot name and are being used and passed.Where did you get the sample as i havent seen one physically.Apparently they are made from GRC is as strong as normal concrete.

sydthebeat

unitjk wrote: »

As far as i know they are part of an approved system which i cannot name and are being used and passed.
.

you may post links to the certification of certain products once it is not seen as open touting for business.

Build Rite

timmer3 wrote: »

hi. i'm getting external insulation (EPS) done to a terraced pebble-dashed house. i got the end wall done a few months ago, and now that the SEI grant has come through i can use that to insulate the front and back of the house. the insulation thickness is 120mm, and this will be enough to completely cover the existing concrete sills, which only protrude about 40mm. my question is do i need window sills at all? i can get the installer to cut a slant in the EPS board to sit on top of the existing sill, to allow the rain to run off. but do i need any overhang? the silicate finish is dirt resistant. i've read about aluminium sills but some say they don't look good, and it seems difficult to remove the cold bridge. i like the thought of insulating all the exposed concrete. i'll be moving the doors and windows out to the edge to help eliminate the cold bridge.
thanks for any comments.

you can build out the sill with the EPS insulation which works very well and is much cheaper.

i dont understand how u got the grant tho without insulating all of the house initially.