have i been caught out on the window opes?

jasperok

Ok - in the middle of a self build. Doing a bit at a time as money allows and learning as i go along though i do try and do as much research as I can.
Where I have falen short however is the window openings.
You see i opted for 150mm cavity at the moment the blocks are finished an the window sills are in.

The next thing to do I think is to fill the gap between the rear of the sill and the inner leaf to bridge the cavity. -
How is this done? with some insulation for support and a piece of wood from behind nailed to the inner leaf to case it and then fill the gap with concrete?

And also the opening itself the gap between the opening there? not forgettting i have an extra 50mm due to the larger cavity. As it is now the Block layers have left it with the 6" DPC down the sides wedged againt the wall with insulation board.

What an earth do i do with the gap?? how is it sealed properly - I imaginne if i get this wrong my wndows will be awful drughty at best and god knows how bad at worst.

Any advice at atll greatly accepted,
thanks

sydthebeat

option 1. You need to get wider cills to bridge the cavity, this depends on final location of windows

option 2. make up forms and cast the soap bars, then fit when set.

option 3. incorporate wider insulation behind cills, and cast soap bar over internal block only, finish with wider window board.

smashey

Wider cills.

edit/ Syd got there first.

jasperok

cheers
but what about the sides of the window opes where the gap between the two leafs is? how is that sealed?

sydthebeat

jasperok wrote: »

cheers
but what about the sides of the window opes where the gap between the two leafs is? how is that sealed?

where is the final location of the window frame...
to the external of the 150mm cavity
or to the interior???

how much of a return block have you?? have you any return block or just lump hammered blocks?

jasperok

by return block do you mean L Blocks?
I forget what the end measurement of an L block is but that is the ammount of block i have protuding into the cavity.
I was envisiging the the window sitting to the external leaf.

sydthebeat

Am i right to say the back of the cill is flush with the inner face of the external leaf?

jasperok

No i think the sill has been laid in relation to the exterior leaf so the window when sitting onthe sill would be closeer to the exterior leaf. however i think this makes some of the cavity gap visible on the inside of the window when you are in the room lookng out.

this only dawned on me driving to work this morning going through the next few jobs in my head, so i am in panic mode as I did not think out the opes and gaps properly and because i am not an experienced builder or window fitter I'm not sure quite the consequences of such a mistake!

250882

Make sure that the back face of the cill is flush with the outside face of the inner leaf of blockwork. The cavity closing block (nib block) only protrudes into the cavity by 50mm leaving a gap of 100mm this can be filled with insulation but the window fixing clips should then be fixed into the outer leaf. Bit late I know but there is also a standard nib block with a 215mm return leaving you with a 35mm gap.
I would still think that the best option would be to keep the outside face of the window frame flush with the inside face of the outer leaf of blockwork as this means the DPCs wont be affected. This will mean that the shape of your cill will change. Remember that because the cill is sitting on a DPC tray the only place it will actually be properly fixed is at the sides so try and make sure it balances correctly on the blockwork.

jasperok

interesting - i'll get up to the site tonight to offer up a window or two and get a better idea in my head how it will pan out.
I guess i am just suprised that its not considered bad practice or wrong to have that cavity at the side of the window- filled with a bit of insulation board and then plastered over that?
isnt it a very week finish or does plaster set harder than a realise?

Mellor

I think you are mixing up the two details. There is no insulation covered with plaster in a standard detail.

The gap at the sill doesn't exist because the sill spans from outer to inner leaf. It only has a bearing of a few mm.

The gap at the sides is covered by a the return block, reducing the cavity to 50mm, The windoe frame covers this last 50mm (which is filled with insulation).

As you have widened the cavity, you should of adjusted these details, wider cill, wider return blocks etc. Infact standard half blocks would of been ok for the return.


Maybe you should post up some photos

blackiebest

Syd, The outside face of the cill upstand should be 25mm in from the internal face of the external block/DPC. See attached. OP you can use the cills you have and span cavity as outlined by syd. You are correct to be concerned about open cavity however use this as an opportunity and insure they are closed tight with as much insulation as possible. Do not forget about insulating cavity in head, very common reason for condensation, and insure your windows are held 10mm off cill, jambs and head and installed using expanding Tape to the outside and loexpanding foam to the inside. In short do not allow eejits install windows. Buy good windows and good luck with the job:)

jasperok

thanks folks thats great info . i have it all clear in my head now.


I am in trouble though as wider return blocks were not used....

ircoha

blackiebest wrote: »

Syd, The outside face of the cill upstand should be 25mm in from the internal face of the external block/DPC. See attached. OP you can use the cills you have and span cavity as outlined by syd. You are correct to be concerned about open cavity however use this as an opportunity and insure they are closed tight with as much insulation as possible. Do not forget about insulating cavity in head, very common reason for condensation, and insure your windows are held 10mm off cill, jambs and head and installed using expanding Tape to the outside and loexpanding foam to the inside. In short do not allow eejits install windows. Buy good windows and good luck with the job:)

BB:Could u tell us where we might source expanding tape/ lo expanding foam pls

jasperok

yes would love to know that too - is there a brand name a building providor might know?

250882

If its the airtightness tape then its a swiss crowd called "SIGA"
They do lots of specialist tapes and adhesives for this sort of thing

jasperok

gap between return block and outer leaf is 10cm
windows are 6cm wide.

what would you do?

blackiebest

Hello all and sorry for not posting info earlier, very busy... HAve a look here http://www.artelit.eu/index.php?app=1&did=98 and the more you read the more you will learn about window installation. It is so important that the process is carried out correctly. Essentially the expanding or 'pre-compressed' tape is not used then the expanding foam will generally extend to the weather side of the window. The plasters will then cut the foam back turning it into a spounge! That is if the installers have used foam at all!:eek: Really many/most window company's do not follow these processes and shlack the window in on a shi*e silicone bed and off with the money. I understand this as all these materials cost money and I estimate up to 4% of my company fitting costs are in fitting materials ( straps/silicone/foam/tape/chims etc) 4% is a lot to any company and mabey that is why the CORRECT processes are not followed. It would never be accepted in other countries and should not be here. Following installation the real problems begin with the so called other trades but this is different subject...:mad:

Sourcing these specialist materials in Ireland I can not advise on, Foam is basic and available in various grades from most good hardware supply stores. The pre-compressed tape is expensive and if anyone wants to source I could offer to post on, PM me. Best of luck,

blackiebest

And for those who want to read more http://www.tremco-illbruck.co.uk/celumdb/documents/Specification_Range_Brochure_GB.pdf

jasperok

sorry to hassle you blackiebest but is there a way of calculating how much tape you would need? for example if i sum up the perimeter of all my opes would i need all that length combined?

so from being up at the site today i can se how my window will sit on the sill and be level with the outer leaf of the cavity, this is where i use the tape as a medium between the window and wall.
On the inside however there is a 4cm gapwhere the cavity is exposed? what would be reccomended here?

one last question is there a better type of foam to use or how does one determine a good/bad foam.

sorry for all the questions everyone, i understand this is why there are proffessionals to do al the certain jobs but sometimes its just not viable to get tehm in.

thanks

jasperok

nice to see that compriband 600 in the pdf - i get how it works now so that solves the how much will i need qestion! i presume you are better off with one or two mm extra thickness than the gap btween your window and wall as its better to have it over compressed thsan not making the seal. i also presume you run it flush o the window and not leave any sticking out.

now to find out will the foam be sufficient for sealing the cavity gap thats there on the inside of the house i know its good to use where the window seals the cavity but no sure in my situation where itwill be quite exposed die to the window not making the seal,

edit
aha
http://www.artelit.eu/z_us/TDS-w&dpro.pdf

maybe i will get away with using that - i wonder will the exposed 4cm on the interior be safe enough to plaster over?