Help - RSJ calculations!

[Dibs-h]

That doesn't mean they can't be load bearing. In some instances, stud walls can be adequate for the load being passed down.

Dibs

 

[wobblycogs]

I'm reminded of an episode of "help my house is falling down" or some such Beeny program I saw. The owners had a stud wall in the middle of the house they wanted to knock down in order to make a larger bathroom. Give Beemy her due she thought there was something suspicious about the wall so had it looked at with a thermal camera - turned out it was holding the roof up! Pretty stupid design all things considered but certainly an important lesson about stud walls.

 

[bosshogg]

Eric...are you telling us that the roof is not turn of the century, but a modern extension?

 

[Eric The Viking]

I'm reminded of an episode of "help my house is falling down" or some such Beeny program I saw. The owners had a stud wall in the middle of the house they wanted to knock down in order to make a larger bathroom. Give Beemy her due she thought there was something suspicious about the wall so had it looked at with a thermal camera - turned out it was holding the roof up! Pretty stupid design all things considered but certainly an important lesson about stud walls.

We have one like that!

There are three dormers on the house. The largest by area is over the stairs. One side is brick to the foundations, the other is lath+plaster. There's a 9x4 beam across the inner end of the dormer (like the other two), with an unsupported span of about 10-12 ft. (roughly square stairwell). This dormer, however bears on the brickwork on one side and lath+ plaster on the other side, The space directly underneath the lath+plaster end is a hollow returning wall on the top floor, and free space for the next two floors down to the ground (it overhangs the stairs on the ground floor by about 2ft).

About eight years ago we decided to replace the two windows in the stairwell, one above and one below the eaves. We found the frames too were load bearing, one down onto the other: The stub rafters between the two windows were tenoned into the lower window's header, otherwise held up by the roof battens nailed on top of them and vestigial (and rotten) "soffit" boards, also on top. What looked like a solid wall running across between the two windows was lath+plaster on the inside and render on the outside, with 'studs' arranged so as to line up with the window mullions. The top window was an aluminium framed replacement put in by the previous owners!

Everything really was holding everything else up.

It's now one single 11ft window vertically, with a steel header (L-section), and a timber frame either side down onto the outer wall at the eaves. I haven't dared consider the inner beam at the top of the dormer. I haven't seen any new cracks recently, so I don't think it's on the move.

Gotta love old properties. :shock:

E.

PS: what's the correct name for the triangular battens right on the bottom edge of the roof that set the last row of tiles to the correct slope? Ours were originally 3x2 cut diagonally. When the place was re-roofed the roofers didn't bother where they were rotten, so the last row sit on the soffits at the wrong angle. I've done every place we've had scaffold access, but there's still a run at the front I haven't got to yet (after 15 years!). Sigh.

 

[Eric The Viking]

Eric...are you telling us that the roof is not turn of the century, but a modern extension?

Nope. As far as I can tell it's all original. The kitchen chimney stack (on the side of a gable) was removed when it was re-roofed. My box room workshop has a small gable which was originally the width of a chimney. That stack has been taken down to the line of the gable roof too, but although it's got Marley concrete tiles now, I think the structural timberwork is all from 1905-ish.

It's an end-terrace house, of three. Oddly, our floor plans are roughly a mirror image of the one at the other end, but the kitchen chimneys were on opposite sides of the respective gables, breaking the symmetry.

Cheers,

E.

 

[bosshogg]

Does the roof contain a ridge board and if so what dimension would it be? Could it for instance support a pair of struts like this

just trying to figure out a simpler system than steel beams...bosshogg

 

[Eric The Viking]

It's a nice idea, but again I fear I don't win :-(

The ridge board is probably about 6x1" or 9x1" - difficult to tell. It is strong and not going anywhere, definitely - there's no sag in the ridge line nor buckling. Apart from it's strength in tension, I've got three issues: firstly it keeps the weight on the roof, which I'm trying to avoid, as I reckon the lower purlin/beams are overloaded; second it's only about 40% of the necessary length (roof is pitched on three sides), and finally (this only occurred to me this morning), I actually can't prop it below to ease the sag out!

Well, technically I might be able to, but it would probably mean Acrows on all three floors, vertically aligned right down to the sleeper walls, and carefully avoiding the decorative plasterwork on the ground floor ceiling. The flamin' ceiling joists in question run the wrong way - a line of props crossing them would only bear on a single floor joist below.

One room on the floor immediately below has a huge sag in it (about 2.5" in the middle), and both have the usual beam across the fireplace (brick arch, etc.), into which the central joists are themselves tenoned. Those heavier joists (with the mortices) are about 1-2ft horizontally away from the centre of the sagging span I want to support. So spreading the load sideways on scaffold boards wouldn't be ideal either. Call me 'sissy' if you like, but I'm not keen to try it.

Deep joy.

I've even got three Acrows on loan presently that would otherwise do it!

This is turning into one of those De Bono puzzles. But then the place has been throwing stuff at us ever since we moved in:

I've redone a lot of plumbing here - almost all the water and most of the heating now. My most 'interesting' discovery was in my smallest daughter's room, above the kitchen. Remember the missing stack? The chimney breast comes down through the corner of her room to where the range was below. Hers evidently had only a small fireplace, but there is still the 'flown' arrangement for the joists, and her window is in the gable end next to the fireplace wall.

So there's me, lifting boards to re-route radiator pipes on the far side of the room. The ones in the landing looked pretty rough (I never notch joists unless it's entirely unavoidable these days - always bore holes centrally, even if it makes getting the pipe in pretty awkward), and I was following a pre-existing pipe run. When I got the board lifted...

... an earlier plumber's mate had obviously spent his first day on the job in that room. The heavy, load-bearing joist was sawn almost half-way through, although only notched by about 1/2". They'd made no attempt to reinforce it, just left it, and put other notches alongside too.

Sigh.

 

[bosshogg]

Last attempt, promise...

Ok, first off if you use 13' scaffold boards as the spreaders, that will distribute the load over 3 or 4 joists! Both top and bottom spreaders aren't required to be in the same direction! To transfer the load to the central LBW I offeryou this -

The purlins should be glued and screwed to the top of the ceiling joists, with the eye bolts bolted through them. The strains can either be galvanised fence wire (if you have an inkling how to do that) or simply 1/2" nylon rope. I have depicted wire with tension sockets inserted one side only, if rope was substituted you would have to put in a tourniquet in there, not so precise but adequate if fixed once tensioned...I think you can get the idea...bosshogg

Imagination is more important than knowledge...
Albert Einstein (hammer)

 

[Eric The Viking]

Last attempt, promise...

Ok, first off if you use 13' scaffold boards as the spreaders, that will distribute the load over 3 or 4 joists! Both top and bottom spreaders aren't required to be in the same direction! To transfer the load to the central LBW I offeryou this -



The purlins should be glued and screwed to the top of the ceiling joists, with the eye bolts bolted through them. The strains can either be galvanised fence wire (if you have an inkling how to do that) or simply 1/2" nylon rope. I have depicted wire with tension sockets inserted one side only, if rope was substituted you would have to put in a tourniquet in there, not so precise but adequate if fixed once tensioned...I think you can get the idea...bosshogg

Assuming the black rectangles are the new purlins, that makes complete sense! I can see too how it would transfer the load to the central wall rather than the roof.

Yup, I do know how to do fence wire - either just wrapped or with what sailors call 'bottle screws' so that wouldn't be too hard.

I think you've beaten it! =D> =D> =D> =D>

E.

 

[Dibs-h]

PS: what's the correct name for the triangular battens right on the bottom edge of the roof that set the last row of tiles to the correct slope? Ours were originally 3x2 cut diagonally. When the place was re-roofed the roofers didn't bother where they were rotten, so the last row sit on the soffits at the wrong angle. I've done every place we've had scaffold access, but there's still a run at the front I haven't got to yet (after 15 years!). Sigh.

I've always heard them referred to as "tilting fillets" - but then again not many folk actually bother to fit them, instead deciding to bodge it with a double lath or one on it's side.

Dibs

 

[bosshogg]

PS: what's the correct name for the triangular battens right on the bottom edge of the roof that set the last row of tiles to the correct slope? Ours were originally 3x2 cut diagonally. When the place was re-roofed the roofers didn't bother where they were rotten, so the last row sit on the soffits at the wrong angle. I've done every place we've had scaffold access, but there's still a run at the front I haven't got to yet (after 15 years!). Sigh.

I've always heard them referred to as "tilting fillets" - but then again not many folk actually bother to fit them, instead deciding to bodge it with a double lath or one on it's side.

Dibs

You're quite right Dibs they are called tilting fillets, and were applied to the bottom edge of the first row of tiles at the bottom of the pitch, so that all the tiles would be bedded at the same angle. Fascia boards were either not employed, as in Scotland, or were planted on to screw rhone/gutter brackets on.
These days of all buildings the tendency is to raise the fascia to achieve the same thing and either use sprockets on the truss lines or omit them altogether with low profile tiles...bosshogg

 

[bosshogg]

Assuming the black rectangles are the new purlins, that makes complete sense! I can see too how it would transfer the load to the central wall rather than the roof.

Yup, I do know how to do fence wire - either just wrapped or with what sailors call 'bottle screws' so that wouldn't be too hard.

I think you've beaten it! =D> =D> =D> =D>

E.

Just glad to be of help...bosshogg

I never teach my pupils. I only attempt to provide the conditions in which they can learn.
Albert Einstein 8)

 

[hanser]

Just a thought. At some point in time you may wish to sell your home. The solution not only needs to do the business but also look professional in order to 'pass' survey. I'd suggest getting galvanised wire strops made to measure, bottlescrews, eye bolts etc. It will look the business and can subsequently be adjusted as you get your ceilings back into shape. As long as you keep away from any supplier that thinks its a ships chandler this stuff is relatively cheap. By this I mean go to an outfit on the edge of an industrial estate that makes industrial slings etc. I can recommend a supplier if you are interested.