RSJ holding up bedroom wall, can it take a loft conversion too?

[perky416]

Hi Guys,

I am toying with the idea of a loft conversion, the new joists in the loft will rest on the wall separating 2 of the bedrooms on the 1st floor. This wall is held up by an RSJ (previous owners knocked through to make a living room/diner). The RSJ measures approximately 90mm wide x 180mm deep x 8mm thick and the span between is about 3.3meters. Aside from getting a structural engineer in is there a way I can work out if this RSJ will take the weight of the wall and the loft conversion? The conversion wont be a bedroom it will mainly be used for storage/an office. I will get a structural engineer in and do the job properly if I decided to go ahead, I am just assessing the project viability. I don’t really want to be ripping the living room apart to replace the RSJ.

Many thanks.

 

[^woody^]

I say no. The bloke next to me on the bus said yes. "Argh", I said "there are several ways to skin a cat". Then he called the Police.

 

[tony1851]

Sounds like a 7" x 4" - that would be OK if the floor spans are not unduly large.

 

[Leofric]

Only a structural engineer who knows all the relevant details of the structure of your house can say. The loft conversion to an office will require building regulations approval and structural engineer's calculations.

 

[perky416]

I managed to find the old data for this beam, it is in fact a 7" x 3.5", the closest universal beam sizes i could find are 152 x 89 x 16 and 178 x 102 x 19. After running the calculations the only issue with the 152 beam was the bending moment. The 178 beam came out fine even with a safety factor of 1.5 for the live load and 1.35 for the dead load. I know the flange is a little narrower on my beam but the web is thicker and it has more mass. I will run the calculations properly for my beam shortly however on the face of it, it looks to be ok.

 

[Leofric]

Who is doing these structural calculations ?

 

[perky416]

I paid for a calculator, that got me the data for the universal beams and calculated the load. To calculate it for my beam the formulas are all over the internet.

 

[Leofric]

As long as you are happy you know what you are doing with the calculations .

 

[perky416]

Havent done this since college but i did mechanical engineering and went onto do level 5 mathematics for engineers. I remember doing beam calculations but havent touched it in nearly 10 years. Itll be done properly anyway this was only to assess the viability. Id have abandoned it if it turned out i had to replace the rsj, now i know i can proceed.

 

[tony1851]

If you have the equations to hand, and are OK with working out the factored loads, the only significant checks you need for domestic steel beams are bending stress and deflection.

Presumably you worked out the bending stress and it's OK? Did you also check on deflection under unfactored loads?

 

[Leofric]

M= fZ Max BM for UDL = WL/8 will leave it with you chaps

 

[tony1851]

M= fZ Max BM for UDL = WL/8 will leave it with you chaps

Question is: how do we determine f ?

 

[Leofric]

Maximum permissible stress in steel, isn't that a figure given in steelwork tables I don't know ,thought you were the structural expert !

 

[tony1851]

Maximum permissible stress in steel, isn't that a figure given in steelwork tables I don't know ,thought you were the structural expert !

Hmmm... it's past my bedtime......