Green Building Forum - Estimate old joist width?

Estimate old joist width?

Osprey — Thu, 22 Dec 2022 12:32:48 +0000

My 1920s house has a kitchen, which used to be a scullery and 'dining room', before the previous owners knocked down the separating wall. The builders installed a large steel to replace the wall. I am planing an extension and wondering if the beam is really needed, as I would like to remove one of the walls upon which it rests, (and have a beam going at 90 degrees for the opening to the extension).

The kitchen internal dimensions are 4.7m x 4.7m. From what I can see through a downlight hole, the joists are around 240mm high, and are about 320mm face-to-face: I cannot see their width.

Can anyone with experience of houses of around this vintage estimate what the joist thickness is likely to be? (Don't worry, I will get a proper structural engineer in before having anything done!)

Estimate old joist width?

fostertom — Thu, 22 Dec 2022 14:56:01 +0000

Almost certainly a generous 2" wide - less wd be unlikely at that date, fatter would be exceptionally strong.

Does the steel run so as to halve the span of these joists? If so, unless there's something heavy bearing on the joists, they're well oversized even without such an intermediate support, at 4.8 structural length and such close c/cs, even if they're floor joists, and doubly over-sized if they're flat roof joists.

Estimate old joist width?

Peter_in_Hungary — Thu, 22 Dec 2022 16:40:47 +0000

If they were 3 x 9s (inches) A typical size for the time and at a spacing of 16" centres, again a typical centring of the day then this gives you 76 mm joist width plus 320mm space between joists = 396mm spacing which is 15.59".

My experience of older house timbers is that they were usually generous in the nominal sizes - that is usually a bit over.

So my bet is that you have 3 x 9s at 16" centres.

Estimate old joist width?

Osprey — Thu, 22 Dec 2022 16:43:44 +0000

Posted By: fostertomAlmost certainly a generous 2" wide - less wd be unlikely at that date, fatter would be exceptionally strong.

Does the steel run so as to halve the span of these joists? If so, unless there's something heavy bearing on the joists, they're well oversized even without such an intermediate support, at 4.8 structural length and such close c/cs, even if they're floor joists, and doubly over-sized if they're flat roof joists.

Thanks for reply.
The steel is about 2m from one end of the joists, so approx 3m from the other. It's where the scullery wall was, and that end is a solid floor. Above are bedrooms.

Estimate old joist width?

WillInAberdeen — Thu, 22 Dec 2022 17:35:44 +0000

Do the joists run 'continuous' over the steel, or are they staggered with 2m lengths on one side of it and separate 3m lengths on the other? Seems quite generous for someone to have put in a steel if the joists could have been self-supporting, the previous generations were more tolerant of saggy floors than modern regs are.

Estimate old joist width?

Peter_in_Hungary — Thu, 22 Dec 2022 17:36:48 +0000

Any walls sitting on the joists?

Estimate old joist width?

fostertom — Thu, 22 Dec 2022 18:24:52 +0000

Guys, this is a 1920s house, when they cottoned on to making joists tall and narrow rather than just adding width for longer spans. 240mm high joist is going to be pretty rigid right to the point of failure - no progressive sagginess. When intermediate support wall removed prob in 1960s, sag wouldn't be tolerated, but 240x50s, prob top quality timber by modern standard, would be plenty strong @15"c/cs for 4.8 length, so Will may be right - they're non continuous - in which case the steel can't be removed.

Estimate old joist width?

WillInAberdeen — Thu, 22 Dec 2022 19:30:10 +0000

Yes indeed! My bedroom ceiling joists span almost that far, and they're approx 2Â½" x 3Â½", at random centres between 15" and 20" and the best part of two centuries old. At some point an electrician has drilled 1" holes through all the joists.

They hold up a floored loft full of boxes of books and a DHW cylinder, and a lath/plaster ceiling. To be fair, it is all a bit saggy, but it doesn't bounce when I jump on it.

Estimate old joist width?

Osprey — Thu, 22 Dec 2022 22:58:13 +0000

Thanks for replies so far.
The joists appear to be continuous over the the beam.

A reason they may have installed the steel is that there is a brick wall separating two bedrooms above. The wall runs in the same direction as the joists (it appears to be actually built on the floorboards...), about a third of the way in from one side, and for about two thirds the length of the joist, very roughly. Now, although that MAY have been the reason, the result is that they installed a pretty meaty steel to support (in practise) the load on one joist, when it would have been simpler and better IMO to knock down the brick wall and replace with stud-partition. Which is what I will do if that solves the problem.

Estimate old joist width?

Coverley — Sat, 24 Dec 2022 09:54:00 +0000

Where are the stairs in relation to this? That beam might also be picking up a stair trimmer.

Estimate old joist width?

Osprey — Sat, 24 Dec 2022 10:24:51 +0000

Posted By: CoverleyWhere are the stairs in relation to this? That beam might also be picking up a stair trimmer.

No, stairs are in different part of the house, thanks.

Estimate old joist width?

Coverley — Tue, 27 Dec 2022 11:44:06 +0000

Also check in the attic to see if anything is bearing on the wall up there

Estimate old joist width?

Osprey — Wed, 28 Dec 2022 12:29:14 +0000

Full width joists in the loft.