Fitting UPVC windows and door in new extension

[seanblee]

Hi all, and apologies in advance for the newbie questions! I'm having an extension built and I've decided to take on fitting the windows and door myself. I've already purchased these (A-rated Rehau white UPVC) and, once the builder gets around to completing the roof (!), I'll be ready to get them installed. The walls are conventional concrete block inner leaf / brick outer leaf, 100mm cavity with full-fill mineral wool insulation. There will be standard cavity closers installed, again when the builder gets around to it. Having read around quite a lot about this, I purchased the windows and door with 180mm sills to allow me to set them further back into the opening, overlapping the cavity closers, to reduce cold bridging. I have galvanised straps to mount them with and I was planning on using the Illbruck i3 system (TP600 Compriband outside, FM330 foam around the frame then ME508 membrane inside) to seal and secure the window in place.

 

My questions are mostly about the sill fixing. I understand I've got a couple of different options...

1. Bed the sill onto mortar first, then fit the window on top - if I do this, given the depth of the sill, presumably I need to put some packers between the sill and the cavity closer to support the back edge, then fill the gaps with foam? Do I need to worry about putting DPC up the back of the mortar and sealing to the bottom of the sill?
2. Attach the sill to the bottom of the window first, then bed onto packers, sealing along the outer edge with Compriband then filling with foam. If I go this route, given the bricks in the window reveal are laid frog up, do I need to fill the frogs with mortar first, or just use extra foam to fill?

 

Do I need to worry about mechanically fixing the sill down to the brickwork? I guess this is more of a concern at the door, where someone might step on the deep sill by mistake. And does the fixing detail change at the doorway? I asked my builder about how he's planning to close the cavity at the door threshold and he just said they'd put a cavity closer then run the screed out to the door once it's fitted.

 

Finally, when it comes to the Compriband, do I fit in in the outer "groove" on the side of the profile? Presumably I need to allow for the depth of this groove in addition to the gap between the outer frame and the masonry when I size the Compriband?

 

Thanks again!

Sean

[Olf]

I'll join the thread with my question. Similar setup: extension, Rehau patio door 3600mm wide, block & block wall with 150mm cavity, thermally broken lintel.

Lintel tech support categorically forbid drilling in the lintel, suggested getting brackets that reach to the inner leaf. That would however require about 400mm long brackets (150mm cavity + 100mm lintel + 100 mm over the edge  to the middle of the block + leftower length of the bracket), whereas the longest Rehau makes are 250mm. Do I really need to attach to the inner leaf to preven flexing, or - considering sides and bottom are going to be bolted to the outer leaf - I'm ok with attaching the brackets to the inner leaf. That will work prefectly well with 250mm brackets. The wall will be rendered, so they won't be seen.

[craig]

On 07/02/2021 at 15:15, seanblee said:

My questions are mostly about the sill fixing. I understand I've got a couple of different options...

 

Option 2, fill with mortar and level out if you can. I would envisage a problem with the packers otherwise.

 

On 07/02/2021 at 15:15, seanblee said:

Do I need to worry about mechanically fixing the sill down to the brickwork?

 

If you can, you want to minimise movement in it as much as possible.

 

On 07/02/2021 at 15:15, seanblee said:

more of a concern at the door, where someone might step on the deep sill by mistake

 

Make sure you pack this cill extension.

 

On 07/02/2021 at 15:15, seanblee said:

when it comes to the Compriband, do I fit in in the outer "groove" on the side of the profile?

 

Yes, that's fine.

 

On 07/02/2021 at 15:15, seanblee said:

I need to allow for the depth of this groove in addition to the gap between the outer frame and the masonry when I size the Compriband?

 

Yes as well as the width of this gap and what your fitting tolerance is. Compriband (7mm to 12mm expansion for example) is only warranted up to the 12mm it is not warranted after this expansion.

 

On 07/02/2021 at 15:15, seanblee said:

using the Illbruck i3 system (TP600 Compriband outside, FM330 foam around the frame then ME508 membrane inside) to seal and secure the window in place

 

OTT for an extension tbh, you don't need to and wasting money. Compriband and PU foam is more than enough (you'd be fine with just FM330).

 

On 06/11/2021 at 15:13, Olf said:

Lintel tech support categorically forbid drilling in the lintel, suggested getting brackets that reach to the inner leaf.

 

On 06/11/2021 at 15:13, Olf said:

considering sides and bottom are going to be bolted to the outer leaf - I'm ok with attaching the brackets to the inner leaf.

 

Yes, don't see why not