Widening knock through on gable

Hi,

I've had a change of plan on the knock-through into our new extension. We'd planned to knock out the bottom of a 2.1M wide window (as shown by the red lines below) and then use this to form a corridor and a door.

Having now got a better feeling for the space, this isn't going to result in a very good design, so we want to widen the knock through to the green lines shown. That would still leave a ~300mm bearing either side for some kind of lintel.

The top part of the gable wall wasn't structural initially (there is no structural ridge on the old house, and the old house roof is supported by two purlins at 1/3 and 2/3 span). Unfortunately the new extension now has a small amount of roof supported by a 152 x 89mm UB which is now supported by this gables inner skin.

What would you do here? The existing lintel is cast in situ with a few lengths of rebar and will be a pig to get out, so I think total demolition of the top of the gable is probably inevitable rather than propping it and slotting a new lintel in. Should I consider getting calculations for some kind of timber lintel and timber frame alternative, or would you just rebuild both skins with blockwork?

Thanks

Why does it need rebuilding?

^woody^ said:

Why does it need rebuilding?

Click to expand...

The only requirement is for something to hold up the end of the 152 x 89mm UB shown in the second photo. That's why I wondered if I should frame it out in timber instead - I have a surplus of 170mm by 50mm timber like a stud wall and would prefer to work in timber - e.g. a beam made of 4x sistered 170mm timbers then the equivalent of a stud wall on top with a king post in the middle to support the UB?

Or spend some money on a UB lintel then a UC to bolt into the end of the UB, but it doesn't feel like a very stable arrangement.

You could support the ridge beam off a post and and beam over the opening, but that means a point load and I suspect an inspector will want calculations of some sort to justify it.

Potentially both these could be timber, but someone would need to calculate it.

Thanks. I'll give it some more thought. I suspect rebuilding both skins with a new cavity lintel might be the simplest approach, even though it's more brute-force and potentially less elegant.