cavity closers to support frames

[gravelrash]

200mm cavity and looking to locate windows 90% over cavity. 1800 x 1325 Alu thermally broken frames with 48mm triple glazing. Anyone know of a cavity closer that supports 120Kg unit?

[Gus Potter]

Any chance of a sketch showing the wall construction, frame thickness and cill detail, will help clarify the 90%? Just draw it on a bit of paper, take a photo and post it?

[gravelrash]

I dont think a sketch is necessary... block masonry cavity walls with eps bead insulation. Hoping to sit windows with 80mm in cavity and 15mm within block opening to seal with expanding tape. sill extends 150mm over block and external cladding.

[Gus Potter]

55 minutes ago, gravelrash said:

I dont think a sketch is necessary... block masonry cavity walls with eps bead insulation. Hoping to sit windows with 80mm in cavity and 15mm within block opening to seal with expanding tape. sill extends 150mm over block and external cladding.

I wish you all the best with your windows.

 

For all.

 

One great thing about BH is that if you give a bit you'll get lots of ideas. Some may not suit (some you may think are .. ? ) you but good design often involves looking at other's designs critically and how they interface with your own home / wall construction... often ruling things out is a great way of reaching an informed decision.

 

Once you get into the 3g (triple glazed) world of windows and aluminium frames with wide wall cavities you have two basic choices. Do we try and transfer the weight of the window to the inner skin or do we look to see if we can use the outer skin to support the weight of the window.

 

Now if you have a wide cavity and aim to use the inner skin to support the window then we need say brackets / a box type liner that are going to resist the cantilevering effect. We need to look very carefully at the fixings and how they will perform long term. In general anything that is cantilevered tends to move a bit more. Windows over time need adjusted / maintained as the glass moves about in the frames and the seals slacken over time. Couple this with cantillevered brackets and you have introduced more potential movement.. and these windows are expensive!

 

If we use the outer skin then we also have potential rotational forces as the outside of the frame only has potentially / commonly  a 15.0 - 20.0 mm rest on the outer leaf and.. we have issues about not breaching the water seal on the cill below as you need to fix the cill to the base of the window frame. We need for example to make sure we keep the drain channel at the bottom of the glass clear.. to prevent the sealed units from resting in standing water etc.

 

But if you have a wide cavity then in some cases you can use the outer skin to support the window, you can remove a lot of the cold bridging effects and rotational / cantilever effects.. much will depend on your wall construction but it's worth exploring to see if it suits you or if you can get some mileage out of it.

 

You can see on BH much discussion about bifiold doors and the options regarding top and bottom supported doors.. imagine your window is a bit the same.. do we bottom support it or try and support it up the sides / bottom with some cantilevered structure?

 

To finish.. BH is also about having a home / extension / DIY project that no one else has! Not just on the outside but also under the bonnet.. the guts of the structure. Don't be afraid to post up a sketch, just draw it on A4 paper, take a photo and post it.. you are not entering a drawing competition. No one here will judge you on your drawing skills.

 

Have fun exploring..

 

 

 

 

 

 

 

[tonyshouse]

Best to support the weight of the window on outside skin masonry, I used steel dowels in the reveal mortar beds to carry the weight and then fixes styles in my case to the back of the outside skin. Nothing has moved, I made my own cavity closers from pir or eps 

[craig]

Cavity closers are not load baring, even the bigblok cavity closers.

 

Do not sit your windows on cavity closers, you’re asking for problems. If need be, outer skin or inner skin or even better, create an 18mm marine ply liner.

Edited November 5, 2021 by craig

[Gus Potter]

2 minutes ago, craig said:

Cavity closers are not load baring, even the bigblok cavity closers.

 

Do not sit your windows on cavity closers, you’re asking for problems. If need be, outer skin or inner skin or even better, create an 18mm marine ply liner.

The ply liner has advantages.. but that is predicated on the fact that the the liner is well fixed to the inner skin.. which is supposed to be plumb assuming masonry inner leaf... and that relies in part on good workmanship.

 

The other thing is that if the ply box is off the square you have a pile of work to do to fix the lining so the margins around the windows look sweet. On Aluminium windows the frames are slender so any out of plumb effects really show up on the finish.

 

On a wide (masonry) cavity wall I would look to see if they can be supported off the outer leaf if the inner leaf cantilever is large..weigh up the options.. each house is different!.. let the window fitters fit, square stuff up and positively fix the frame.  Then do the finishing to get an even margin around the windows.

 

Just as an aside if you have a timber frame (TF) on the inside then this fixing to the outer leaf is a non starter in my view as the TF moves about up and down by a fair bit. In other words the window is fixed / stays still as is fixed to the outer masonry leaf.. on the inside the TF is going up and down and this will not look good when viewed from the inside!