Bay windows for complete beginners

[MortarThePoint]

Is there a rule of thumb as to how the side windows should open? They can either be hinged on the house side of the bay elevation (option B) or on the other side (option A).

• Option A: hinged on side away from house, opening gap nearest house, you see the outside of the window sash when looking at the front of the house with the windows open
• Option B: hinged on side closest to house, opening gap away from house, you see the inside of the window sash when looking at the front of the house with the windows open

I can see you'd get more ventilation with option B. There must be a way this is normally done

[Gone West]

I would go with option 'B' because I care more about functionality than aesthetics and if the sashes are opening then they should let in air. IMHO option 'A' makes me wonder why they are opening sashes and not fixed. Just the way I am. 

[MortarThePoint]

On 10/09/2021 at 20:16, PeterW said:

Just use bay pole jacks - you drill through the cill and they rest on the brickwork below. Pretty standard detail that any FENSA manufacturer/installer will specify.  

 

Gearing up to do this. You're right, it is bay pole jacks and they are rated for plenty of weight. What's the normal installation sequence? The central window (3m wide) is very heavy and it would be very difficult for that to not me the first item put in place and braced bay poles are installed with the side windows. But that presupposes the sequence. I then imagine the head timbers being built on top of the bay poles and then the rafters cut in.

[MortarThePoint]

Windows came with Bay Poles and Bay Pole Jacks by Window Widgets. Their catalogue says they are rated to 2t (I think)so plenty of capacity there. An important thing to remember is to check them at the end of the installation as the bay pole may have crept off a tight seating and so the bay pole load would be left being carried by the windows not the jacks which would not be good.

 

We had pretty smooth and level brickwork already, but I lightly touched it with a grinding cup to get it very flat and tweak level too. Need to allow some wiggle with the bay pole jack position as their position ends up defined by the window(s)  (the large central window in my case). For me the cill was predrilled (Window Widgets suggest 20mm which I guess was what I had). It would be good to have a washer (guess M12 or M14) to put over the bay pole thread and to rest on the cill as that would help with the subsequent sealing. I had a large gap as no washer so glooped it up a lot.

 

[MortarThePoint]

Lifting and moving the large central window was something I had dreaded. 3105mm x 1460mm so heavy and unwieldy. I roped in 3 friends the wife helped too. We had to flip the window as well. Carrying the window out of the house was the hardest bit and we used straps under the window and carried it out to trestles (strong). We couldn't use anything going under the frame for the final placement, so I put a short length of batten through the loop the window manufacturer had put on each end of the window. I don't trust such a loop to lift a large window like this so also screwed the small bit of batten to the frame (2no 5.0 x 50mm). I then screwed a piece of 4x2 across the front and back of the window with a block at each end for the screws to go into. This gave us convenient handles at a good height to do the precision lift. The wife guided the window into position using rubber window suckers (no force just precision). We got it spot on and the final lift was a breeze. I had rigged some timber braces to swing down onto the top of the window to stop it falling and the whole operation took less than an hour.

 

 

[Gus Potter]

9 hours ago, MortarThePoint said:

Lifting and moving the large central window was something I had dreaded.

That's looking good.. everthing looks nice and clean. Nice brickwork / blockwork, lead flashings not over length (as per Cookson guide to good leadwork), good drip (min 40mm recommended) on the cills. Looks like a clever detail at the bottom of the wall abutment flashing.. any chance of a close up photo?

 

Well done I say.

 

For all. In principle you can stick a lot of load down a short strut bay pole before it buckles. Hence the two tonnes mentioned.

 

But when the manufacture's test these they work on the basis that you have a material top and bottom that has a high compressive strength and is stable side to side (laterally) which is not often the case as you may have brickwork below and timber above.

 

SE wise I would always look at any bay pole visually. Any more than 200 kg load say invites a fag packet calculation check on the suitability / stability of the materials that are above and below it.

 

In summary.. if you are putting more than say 200kg down a bay pole then don't take just the advise of the window fitter, always use common sense and look at what is below it.. old brickwork, soft stone.. and what is transferring the load to the bay pole at the top.. say timber... let common sense prevail. Also remember that what is above and below may want to move sideways as it is essentially "balanced on a pole" so you need to take measures to prevent this.

 

Remember that if the material starts to crush a bit at the top and bottom of your bay pole load will be transferred to your new windows which may start to "protest".

 

 

 

 

 

 

 

 

 

 

[MortarThePoint]

18 hours ago, Gus Potter said:

That's looking good.. everthing looks nice and clean. Nice brickwork / blockwork, lead flashings not over length (as per Cookson guide to good leadwork), good drip (min 40mm recommended) on the cills. Looks like a clever detail at the bottom of the wall abutment flashing.. any chance of a close up photo?

 

Thanks, I'll try to take some more photos.

 

18 hours ago, Gus Potter said:

SE wise I would always look at any bay pole visually. Any more than 200 kg load say invites a fag packet calculation check on the suitability / stability of the materials that are above and below it.

 

Makes sense, pole is good but need to be sure everything else is sound too. The total weight of the bay roof will be about 600kg (6.5m2 of tiles = 500kg). The timber against the face of the house will be taking some of the load but I expect the bay poles probably take more than half, so perhaps getting on for 200kg each. There will be a substantial beam (8x2 2ply shown purple below, 3m long) across between the bay poles which most of the rafters will bear on. At the sides it's less clear, but I am thinking I'll make a simple 4x2 frame (blue with some 2x2 as well) and use frame fixings to attach one side of it to the house brickwork (red lines). The bottom and top chords of these side parts is a 4x2 on edge backed by a 2x2. I thought I'd use the 2x2 rather than 4x2 on the inner side to allow more insulation. The front beam is 3m long so has quite a bending moment, but those side frames are only about 600mm, so not much moment I figure. Additional 4x2 and 2x2 frame work in orange above the purple front beam to make up the height and allow insulation infill. Bay pole positions shown in green.

 

I had originally planned (even bought some) to use a masonry hanger for the side frames, but they typically cut into the brickwork and don't provide any lateral constraint. I can see one made by Parkes that is face fix, but can't see where to get it from and it feels like the 4x2 bolted (7.5mm frame fixings or M8 bolts) to the masonry will be just as secure. The rafter closest to the house wall will be bolted to the house wall so the vertical load carried by these side frames will be quite low. I am more concerned about the lateral constraint.

 

 

 

 

[MortarThePoint]

I think it would be better if the top frame (orange) had the 4x2 on flat as that should stiffen the assembly against lateral forces. The ;studs' on 600mm centres should easily be able to take the weight of the rafters bearing on the top 4x2. I could position them to coincide with the rafters as well.

 

 

Edited November 1, 2022 by MortarThePoint
Better diagram