Increasing window width, lintel needed?

[ajay16]

120/150ish year old outbuilding, brick and lime mortar, pantile roof, wooden trussed with a wood (I gather oak) top plate all the way around.

I'm increasing the size of this window to 117cm non-opening UPVC from a frameless opening 81cm wood window, the window sits below the top plate.
I don't really want to put anything concrete based into the building.
Likewise ideally I don't want to lower the current height of the window either, but, do I need any sort of extra support?
If so, any ideas what?

Before undertaking the renovation i've tied every truss to the top plate with truss clips or hurricane ties, so everything should be pretty solid in that regard.
I also didn't go too huge with the window to hopefully negate the need for a lintel.

 

[LeonUk]

If you want to avoid concrete, my routes would be: (1) a sized oak lintel set just under the top plate (min ~150–200 mm bearing each side, packed with lime mortar), or (2) twin galvanized steel angles (legs down), similarly bearing into the brickwork and hidden behind the reveal.
Either way, prop the wall while you cut, and keep everything in lime.

 

[Cubist]

What are the width snd depth dimensions of the top plate and how good/bad is the condition of the timber itself? Have you checked for any dip or sag?

 

[ajay16]

No dipping or sagging that I can see anywhere.
The building also has four other windows in it, all are cut straight into the brick, the windows sit below the top plate beam. Wood frame, fixed, non opening.
The widest one is 80cm long.

Top plate is roughly 80mm wide, by 70mm high.
Some woodworm holes in places, one section (other side of building not near a window) is quite powdery due to previous woodworm, roughly 10mm deep from the surface.
All the top plate has been treated with woodworm killer and preserver just in case, but it all looks very historic.

 

[Cubist]

The plate, at roughly 75-80mm square, would be considered a little light for carrying unsupported loads over more than a metre or so in most buildings but in a single story outbuilding it may not be uncommon. Would I be correct in thinking your plan would include the placement of two wooden posts at the sides of the new window into which it would be fixed? Or are you hoping to fix the UPVC frame directly to what would become the outer brickwork? I would be a little nervous of the latter.

I note that there is what appears to be a piano hinge running along the top inner edge of the current frame so I'm assuming that at some point the window may have opened inward. It may be an idea to remove the hinge to determine whether the top edge of the frame is tightly pinched under the plate. If it's very tight then the plate has perhaps sagged slightly which may then suggest that complete removal of the frame could result in a further downward movement. If it's loose and you can run a thin blade between the plate and the frame then you're largely good to go. Either way I would suggest that you consider installing a flat steel bracket fixed to the inner face of plate and longer than the proposed opening. This would stiffen the plate against any further movement without any appreciable loss of space indoors.

 

[ajay16]

Thanks for the input

I'm open either way to fixing the window, initial thought was to go straight into the brickwork as the walls are pretty thick at 200mm.
But if it needs supports then the next option would have been some timber to prop up the top plate.

As LeonUK said though, adding some steel angle on the inner side in the reveal could do the same job without the worry of woodworm over time.
Something like 50mm x 8mm.

It's hard to tell with the hinge as it's not the best job, i'm not entirely sure if it's ever closed fully, hence the chicken wire mesh and frame on the outer side and missing brickwork.
I'll definitely give it a measure at each ends then work towards the middle to see if it has sagged.

Will order some steel for the inner plate face whichever way I go as that sounds sensible.

 

[stuart45]

The roof looks to me like it's sagging a bit over the window, but it could be the photo. As you've got point loads on the plate from the roof loading, it's more than if you had brickwork over the top spreading the load. Roof plates are designed to spread the load evenly over the masonry, but not really act as a lintel. With snow and wind loading, the point loads from the rafters can be quite high. Most houses had 6 inch concrete lintels over the upper floor windows before Catnics came in.

 

[ajay16]

Ok...so maybe a steel T lintel, inner side would go under the wood wall plate, and the outer side can support a row of bricks to finish off the reveal?
Or potentially an angled L lintel on the inside supporting the wall plate - as it will be covered over by wall framing.

(Roof tiles are all over the shop due to slipping over time, no sagging on the roof)

 

[stuart45]

You can always ring Catnic for their advice on whether the CN50 is suitable for what you want.

 

[Cubist]

Somethings been nagging at me..... if that's a 9inch, circa 230mm (2 bricks wide) wall, why does the timber plate appear to sit flush to both the exterior and interior faces of the wall?

If the plate is a single timber then surely it would be in the order of 230mm wide?

 

[ajay16]

Alas, that exterior piece of wood is just a ruse! (Actual wall plate is behind it in the pic).

It just sits there for show, i don't even think its fixed in as there should be a row of bricks above like the other windows have.

It's really been done incredibly badly, many, many, many years ago.

 

[stuart45]

I thought the same as cubist. Can see it a lot clearer now. A CN50 would probably got in there nicely, although not cheap at around £100. It probably would be worth doing something like that, as replacing timber frames with plastic often causes issues with the frames deflecting and cracking the glass or jamming the frames.

 

[ajay16]

I'll need about a 160cm lintel allowing 20cm each end, so it's about £200 delivered for a CN50.

I could do similar with two sections of galvanised angle, structural spec for £120.

Ideally I probably need to do the same on the other side with the 80cm window too which is being replaced like for like size wise just in UPVC.

 

[stuart45]

That's gone up in price a lot since I last bought one, which was only a few years ago

 

[ajay16]

Catnic said there isn't enough headroom to use it...

Back to chunky galvanised angle.
Will try and update the thread once all done.

Cheers for the advice everyone!