Window fixing into stone arch

[saveasteading]

We have some characterful stone arches. Another way of saying wonky...they have moved over the years and are not symmetrical.

That is the glory of arches, they move, adopt a new shape, and keep working.

 

So our new windows are asymmetrical too. They are upvc frames, made with 4 different straights at the top to replicate the curve at a fraction of the curved cost.

 

To the sides and bottom we will plug and screw. But I am conscious that the arch may move again.

How to fix to the top? If screwed through then any joggling of the stone and the screws will push or pull at the frame and will likely crack the glass. Or thd screws inhibit the movement of the stones.

 

Perhaps just expanding foam as glue, and no screws. How flexible is it? I suspect it crushes but doesn't expand.

Or memory foam strip?

 

My inclination is to make slip brackets of 2 angles with a slotted connection, then fill with quality expanding foam and/or memory foam.

There should be 20mm top gap at the joints, and wider between (straights under curve).

[Miek]

3 hours ago, saveasteading said:

 

Perhaps just expanding foam as glue, and no screws. How flexible is it? I suspect it crushes but doesn't expand.

Or memory foam strip?

Use Illbruck FM330 foam. It's airtight and remains flexible, Brilliant stuff.

Edited November 9, 2022 by Miek
Spelling

[saveasteading]

13 hours ago, Miek said:

remains flexible, Br

Does it expand after curing though if, as arches do, one stone moves up a fraction in a year or so?

[saveasteading]

Thanks Miek and to everyone else who didn't respond.

No I am not being facetious.

One of the great things about this forum is that people don't guess, and don't reply to say they don't know...which I just hate on other forums.

 

I have had great advice that I have acted on, some that i have absorbed and then not acted upon, and the occasional silence. The latter is always on complex or very particular circumstances. Silence confirms that my ideas are as good as anybodys..... probably, and is all my own problem.

 

So the decision is made, and is to not use mechanical fixings up to the arch. Fixing will be by quality expanding foam.  We will probably first insert expanding foam tape to the outer edge as a permanent and flexible weather seal.

 

For general intrest, the bulk of the units are Nordan: timber windows with aluminium outer skins.

They couldn't handle angles or curves*, and are a bit clunky at multiple units, so these are coming from Stevenswood. Upvc with a coloured outer skin, and so very much cheaper.

* a series of straights....3d bit style......not seen yet.

 

 

[Miek]

10 hours ago, saveasteading said:

Does it expand after curing though if, as arches do, one stone moves up a fraction in a year or so?

If it expands after curing it won't exert much force as it remains permanently flexible, I really doubt it could lift an arch.  When cured you can squeeze it like a dense foam and it springs back. 

[saveasteading]

14 hours ago, Miek said:

When cured you can squeeze it like a dense foam and it springs back. 

That was what I meant. Reclosing the gap.

Window going in soon so i will report back.

[Dave Jones]

you could also move the mechanical fix off the frame by using  frame straps, added bonus of no holes visible from the inside.

 

The ilbrook foam is very good.

[saveasteading]

7 hours ago, Dave Jones said:

you could also move the mechanical fix off the frame by using  frame straps, added bonus of no holes visible from the inside.

Could you explain further please?

 

A short strap inwards onto the stone jambs is ok because we will fit a timber plate into the junction. But we want to leave the stone exposed as much as possible. 

Pleased to say that the bco has accepted the stone being exposed internally, locally as long as  we trade off with more insulation elsewhere.

[gaz_moose]

what he is suggesting is to use a frame strap, so you don't have to drill through the frame. on upvc windows they clip into the edges of the frame (that face the brickwork) and then you screw then to the inner wall which would then be plaster boarded over.

 

tbh i would go with concrete screws straight through the frame into the stonework and decent expanding foam.  the fischer ones with the built in rawl plug are old hat nowdays. (im no upvc expert BTW)

 

 

Window Fixing Clips / Door Fixing Strap (6pk)Schuring 70mm UPVC Window Systems | eBay

[Dave Jones]

14 minutes ago, gaz_moose said:

what he is suggesting is to use a frame strap, so you don't have to drill through the frame. on upvc windows they clip into the edges of the frame (that face the brickwork) and then you screw then to the inner wall which would then be plaster boarded over.

 

tbh i would go with concrete screws straight through the frame into the stonework and decent expanding foam.  the fischer ones with the built in rawl plug are old hat nowdays. (im no upvc expert BTW)

 

 

Window Fixing Clips / Door Fixing Strap (6pk)Schuring 70mm UPVC Window Systems | eBay

 

yes this, they overcome the majority of the frame now sitting within the insulation which makes it hard to smash a 100mm conc screw through the lot.

[saveasteading]

2 hours ago, gaz_moose said:

concrete screws straight through the frame into the stonework 

For the timber windows into stud we used straps into timber frames and they will be concealed by plasterboard

For the aluminiums into stone we are  going with plug and screw through the frame into the walls. This provides a little more give than concrete self tappers and I have found the premium plugs to be very good .

As we are screwing straight into a 600mm ashlar sandstone wall there is no insulation layer to concern us. Then to the top: expanding rubber(like)  seals to the front (if the frame will allow) then high quality foam behind.

No mechanical fixings to the arches.

 

Unfortunately the window supplier has provided link strips that are different colour to the windows...so another delay until I can report back.

 

It is fair to say that the bco is being very helpful. He clearly likes what we are doing and appreciates that leaving an extensive cold bridge* (some masonry exposed internally) is reasonable for aesthetics and heritage. He also spotted an issue with headroom for the stair....in good time before it was made. Impressive.

 

*We can readily add some extra fibreglass in the attic to offset this scientifically, and burn a few more homegrown or scavenged logs in reality.

Edited November 17, 2022 by saveasteading
clarity