225mm cavity - How to install windows?

soldsold

Any opinions appeciated on a job I have been thinking about for the last few months... I have a 225mm cavity wall (100mm block, 225mm cavity, 100mm block) and still unsure how to install the windows - they are triple glazed and some are 1.8m and 2.2m wide, triple glazed aluclad so big and heavy.

Im considering resting them on the concrete sills that are set 50mm into the cavity, ie balanced on the outside blockwork with a 20mm gap between the inner surface of the external block and the upstand on the sill.

I'd like to minimise cold bridging and save 4000 euro by not having to use thermally broken timber frames, but my main concern is installing in a way that wont cause sticking windows/ moisture/ cracking plaster reveals/ cold bridging condensation issues.

As I cant get the windows I want in Ireland at a reasonable price I will be importing direct from Germany, so I'll have to install using a local window fitter that has no experience in 200mm cavities/ cold bridge reduction.

Just to add to the task, some of the windows have a 30 degree angled window reveal on the inside reveal, and this angle is cut into quinn-lite blocks (obviously a bit brittle compared to dense blocks), this is leading me to think that resting the windows on the sill and strapping to the outside blockwork is the way to go.

Any thoughts?

Thanks!

dannyhandy

i have fitted many windows all over ireland and england. fitting windows with a 200mm cavity it not really a problem if done right it just comes down to experience, if your fitter have not done it before you should get someone that has otherwise you do risk the plaster cracking and have problems in the future

soldsold

Im surprised anyone has experience fitting windows into a 200mm cavity as there are very few wide cavity builds that have been built. Any details on how you would do it? Strap to inner blockwork or outer blockwork? Insulation between window frame and outer blockwork? How to stop the plasterboard joints from cracking?

thanks!

dannyhandy

where are you based? if your local i could come and show you on one of the windows

soldsold

Birr Co Offaly...

gman2k

soldsold wrote: »

Any opinions appeciated on a job I have been thinking about for the last few months... I have a 225mm cavity wall (100mm block, 225mm cavity, 100mm block) and still unsure how to install the windows - they are triple glazed and some are 1.8m and 2.2m wide, triple glazed aluclad so big and heavy.

Im considering resting them on the concrete sills that are set 50mm into the cavity, ie balanced on the outside blockwork with a 20mm gap between the inner surface of the external block and the upstand on the sill.

I'd like to minimise cold bridging and save 4000 euro by not having to use thermally broken timber frames, but my main concern is installing in a way that wont cause sticking windows/ moisture/ cracking plaster reveals/ cold bridging condensation issues.

As I cant get the windows I want in Ireland at a reasonable price I will be importing direct from Germany, so I'll have to install using a local window fitter that has no experience in 200mm cavities/ cold bridge reduction.

Just to add to the task, some of the windows have a 30 degree angled window reveal on the inside reveal, and this angle is cut into quinn-lite blocks (obviously a bit brittle compared to dense blocks), this is leading me to think that resting the windows on the sill and strapping to the outside blockwork is the way to go.

Any thoughts?

Thanks!

Wow, that's a big one!
What cavity insulation have you used?
And how did you go about tying the two leaves together?
Thanks

soldsold

Pumped ecobead insulation, vartry engineering wall ties (straps) at 450 x 450 centres.

gman2k

soldsold wrote: »

Pumped ecobead insulation, vartry engineering wall ties (straps) at 450 x 450 centres.

soldsold - what's your u-value for that wall construction? and are you going to use insulated plasterboard also? thanks

soldsold

I'm planning EPS insulated boards on the North and East walls (15 euro compared to 24 or so for PU boards).

Sorry I have forgotten the u-value this wall will give, maybe someone else can calculate it along with advice as to how to hang my windows

sesswhat

Presumably you have some sort of temporary former in place already. This leaflet suggests placing the window in a permanent plywood liner. See from page 5 onwards.

soldsold

Thanks for the reply, the link is very useful. I had seen it ages ago and it fits in with a couple of passive builds completed in UK so maybe this is the way to go. I had concerns about plywood long term but having 3 references showing it as the preferred detail (the other two are tonyshouse.info which Sinnerboy pointed me to, and the Denby Dale passive house Bill Butcher has just finished). Its also the detail that this forum member 'beyondpassive' advised me to use at the start of the planning stages, so maybe full circle to the original plan is the way to go.

I dont have any formers in place but cant imagine building plywood boxes will be a lot of work for my carpenters.

Cheers,

Steve

gman2k

soldsold wrote: »

I'm planning EPS insulated boards on the North and East walls (15 euro compared to 24 or so for PU boards).

Sorry I have forgotten the u-value this wall will give, maybe someone else can calculate it along with advice as to how to hang my windows

Cheers - You prob know already, make sure all elec cable are conduited and don't come into contact with the EPS insulation.

cosatron

ive just installed rationel aluclad windows, and their windows were sitting about 20mm into the outer leaf as to let the window breathe. therefore with a 75mm thick window, the cill will have 160mm of insulation behind it and the cill will be relying on 1 leaf of block work. Also what about jamb details, will be using L blocks. With the cavity so wide, will it be a hard to get your dpcs right,
Have you talked to your engineer or architect about details.

soldsold

cosatron wrote: »

ive just installed rationel aluclad windows, and their windows were sitting about 20mm into the outer leaf as to let the window breathe.

Do you mean 20mm gap between the window and the inside edge of the blockwork (like I am planning), or resting 20mm on the exterior blockwork?

cosatron wrote: »

Also what about jamb details, will be using L blocks. With the cavity so wide, will it be a hard to get your dpcs right,
Have you talked to your engineer or architect about details.

Lots of head scratching to make sure the detailing is done soundly, Ive also considered wrapping 200mm insulation in DPC to close the cavity. Im hoping the Engineer wont have to come up with the answer and I can suggest something I am sure will work, and that he will be happy with.

Is there an issue with strapping windows to the outer blockwork, with a 20mm insulation gap between the window and the outer block?

Either this, or building a plywood box seem the two most logical ways to do the job. I cant imagine trying to hang heavy triple glazed windows off an inner leaf of 4 inch quinnlite blocks with a 30 degree angle cut into them...

Ignore the doubled-up lintols in the photo please, I didnt know this was a bad idea until the blockwork was complete!

cosatron

20mm to 30mm on external leaf,see detail attached, but other companies are different. its not recommended to strap the windows to the other leaf, always strap to the inside, you should've used L-blocks on the window edges, it looks like your going to have to wedge in pieces of timber for a fixing for the windows and trying to close the cavaty on the edge with the dpc is going to be tricky.. The window cills are going to be a complete nightmare, are you getting cills specially made up,

soldsold

Thanks for the drawings, I didn't use L shaped blocks as the window reveal has a 30 degree angle so L shaped blocks wouldn't work.

The concrete exterior window sills are in place since the photos were taken, they are set into the cavity 50mm (25mm gap from exterior blockwork to the lip at the back of the sill, then 25mm lip). Basically the sill is balanced on the exterior block and cemented into place. I have been planning to rest the edge of the frame on this lip with the aluclad hanging down over it to protect from the rain.

Inside window ledge will be poured in concrete and probably a painted MDF ledge made to suit.

soldsold

This is what I have at the moment...

dfader

Soldsold,
Im bumpimg this one cos I am considering a wide cavity for my new build.
I have been struggling with this detail. My thoughts on it are to support the cill with some sort of metal cill supports under across the cavity and return the block in the reveal as you are building up the blocks (closing the ope with block, using AAC blocks) rather than closing them after as you are doing. I am not appealed by the plywood closer.
I know this suggestion doesnt really help you now but I am very interested in seeing your solution.

soldsold

Still working on it dfader.

The greenbuildingforum in UK is having an interesting discussion on this at the moment, and the AECB also in UK seem to have published some guidelines (see reference in greenbuildingforum thread here: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5349)

The two passive/ zero energy houses I had been looking at in UK both used plywood boxes and Knauf technical guy replied to my email during the week to say that is still what they recommend.

I'll definitely document the way I go through pictures and song.

Well pictures anyway.

dfader

Hi Soldsold,
Hope the extension is going well.
Was following this tread with interest and wondering how you closed your cavities in the end and fixed your windows. Would be great if you could update this tread some time with your finished detail. Pics would be great too if you have any.
regards,
dfader