Steels needed on Hip to Gable with rear dormer on Bungalow

[Elthrin]

I have a 1935 bugalow which had a loft conversion in 1965, this consisted of a front and rear dormer.

I have already added a single storey rear extension myself including the the planning and building control applications. This all seemed straight forward but adding a ensuite for the loft conversion is next on my list.

The plan is to use the loft area left below the hip to create the space for the new shower room. With a door through from the existing extension. My question is do I need to put in a steel RSJ for the new ridge or should I just extend the existing ridge board out the extra 3m to the new wall I will be building?

I know building control seem to be obsessed with RSJs so I am happy to put one to rest the dormer on but I really don't see what good one will be in the ridge. Am I missing something?

 

[Elthrin]

Untitled

• Elthrin
• 17 Apr 2012
• 1

Untitled

• Elthrin
• 17 Apr 2012
• 1

 

[tony1851]

Are you going to actually build a flat-roof dormer, (say, on the rear slope) or just replicate the shape of the existing roof?
If you are only extending the planes of the front and rear slopes out to meet a new gable wall, you could simply extend the ridge board without steel.
If you built a dormer, you would then need a steel beam at ridge level, spanning between your new gable wall and the party wall. This would be necessary to support the flat roof on one side, and the sloping rafters on the other.
(You will probably need some steel beam(s) in the floor, though).

 

[Elthrin]

Yes I will be adding a dormer at the back. Agree about the floor.

I understand what you are saying, and I suspect that is the most usual way of doing things these days. The issue I have is that I dont have access to the party wall due to the previous extension. and even if I did the beam would have to go through the chimney breast.

Is there some other way I could do this?

 

[tony1851]

Is there any internal load-bearing wall on the ground floor, that you could build over in the loft, to support a steel beam? eg with studwork. It wouldn't have to exactly line up under the end of the beam because the steel can cantilever over a little.
A sketch plan showing ground floor layout (with load-bearing walls shown) plus layout of how the loft is proposed, would help.

 

[Elthrin]

The existing conversion stops on top of a load bearing wall. Do you mean I could build up from this and have the bean sitting on walls both ends?

 

[tony1851]

If the conversion has a stud wall built over an existing loadbearing wall below, that could well provide a useful support for your steel ridge beam. Some inspectors will say you can't support a steel beam off studwork but you can, subject to certain conditions; it might just need beefing up a little, eg with some plywood or OSB to provide lateral stiffness.