Loft Ridge

[Mastercraftsman]

Hey guys, please excuse the silly username, made in jest!

Im currently undertaking a loft conversion at my home, its a 1930s mid terrace, im putting a large rear dormer in.

Most of the steels are in now, two 5.6m 203x203x52 UCs span from party wall to party wall. I have the floor minus the trimming in and today appeared to be a good day to get the ridge beam in.

The engineer specced a 152x152x37 sat at one end in the party wall and at the other end bolted to a 100x100c24 post via a 100x100x8 cleat. This post is to sit the ridge off of the two flues of the chimney coming up from downstairs. This post bears down on a load bearing wall .

As I broke into the party wall I discovered that it was only 1 skin thick, where it backs onto the neighbours flue. (I had no problem with the 203s it was double skin and in good condition)

From what I am aware, putting a ridge beam into this would be a big no no, so thats out the question, what other options do I have? I guess I could span another steel from one 203 to another 203 , however there is no loadbearing wall this side as it is above the stairs below and the steel would need to be approx 6.7m long.

Is this a viable option? I can see that if it was it would look weird when the stairs get built from the first floor to the loft with a large boxed in section along a certain part of the wall ? I know I will need to speak to my engineer, but its playing merry hell with my mind and I was wondering if anyone had any possible solutions until I hear back from him?

Smiles,

 

[tony1851]

When a steel ridge beam is to be supported off a 1/2 brick wall backing on to a flue, a way to support it is to bolt a vertical piece of 100 x 100 box-section steel to the wall, with an angle cleat at the top drilled and bolted to the underside of the steel.
The box section should be about 1m - 1.5m long, with equally-spaced lugs welded on to the back, with 17mm holes drilled into the lugs, so that the post can be bolted to the brickwork (16mm bolts or threaded bar into whole bricks only - not mortar).
If you have three equally-spaced lugs on each side of the post, it will distribute the load across the brickwork and the stress on the wall won't be that great (roofs are not heavily loaded). The bolt-ends shouldn't penetrate nearer than 40mm to the flue, so with 10mm thick lugs, bolts should be around 70mm long. Use chemical fixing - not expanding bolts.

 

[Mastercraftsman]

Thanks Tony, that all makes perfect sense! Is it something that would need a calculation or is it something that a BCO may just agree and sign off on ?

Would you also be able to offer some advice Re: the post at the other end which is bolted to the 100x100 post at my chimney end please ? My engineer has drawn the post to sit within a solid wall spanning the front face of the soon to be created dormer to the rear purlin wall which is sat on one of the 203s . I would like to try and keep the chimney visable but my engineer was concerned about the forward thrust of the highway facing roof hip , I believe he wanted the post in a wall to prevent lateral movement. I have seen examples where a steel has been used as a post and that post remains visable within the room but this means the chimney can be exposed as it is no longer hidden by the posts lateral wall.

I have attached a pic to show you watch I mean, do you think it is possible to have this exposed with the post or should I be looking to switch this post to a steel ?

Smiles

 

[tomfe]

Think of all that dusting!!

 

[Mastercraftsman]

Think of all that dusting!!

haha indeed! thanks I will point this out to my Mrs this evening who is championing the exposed look !

 

[tony1851]

I have never been asked to do calcs for a box-section support bolted to the chimney front. In any case, it's difficult to quantify because you won't know the crushing strength of the brick immediately under each bolt, where the weight acts; it just 'works'.

For the other end, I can't see why the SE is concerned about lateral support against the push from the hip. The rectangular flat roof of the dormer will offer sufficient support (it acts like a horizontal rigid plate once the deck is nailed down). The flat roof maintains its shape and so resists the twisting moment caused by the hip. In any case, the forces involved are not great.

 

[Mastercraftsman]

fantastic thanks Tony , everything you say makes perfect sense, hopefully the BCO will be on board !