Adding a lintel for new doorway and BC signoffs

[RScorpio]

I am considering creating a new doorway in a central load bearing wall in my terraced house on the first floor, as a new entrance to one of the bedrooms. The internal wall is single brick lined about 15cm thick with plaster, and rests on top of a beam which is in my living/dining room. The wall supports the ceiling joists for my bedrooms and also the timber struts for my roof.

This layout is a good example for the above description in my house. https://www.beamcalculation.co.uk/calculations/beam-supporting-internal-wall-roof-ceiling-floor

I want to move my existing staircase which runs in the middle of my living/dining room to run along the side of a wall to open up the space, which is why I would then need to create a new doorway as well.

Firstly the steel beam has been there for a good number of unknown years, and was put in one of the previous owners. It doesn't seem to have any building control signoff.

Now since I want to add a new doorway in this central wall I am not sure if I need to get retrospective BC signoff and structural calcs done before I can consider moving the staircase and adding a new doorway? The above website can give me some calcs but I am unsure if I can anyway check if the beam specifications meet or exceed this.

I do intend to get BC approval for the staircase move and new doorway, but the existing steel beam worries me if this will cause me trouble.

With the new lintel for the doorway do I then need some further structural calculations done for what needs adding here or can a standard 1200mm reinforced steel concrete suffice of this type suffice?
https://www.jewson.co.uk/p/supreme-concrete-prestressed-lintel-r15120-1200-x-140-x-100mm-LNBRN155
I would be grateful if anyone can advise. Thanks.

 

[sxturbo]

Get an se round to have a look and do some calcs.

You can cross check his calcs with that website and hopefully be there or about.

That's the only logical thing to do.

 

[Dereekoo]

Re the lintel, based on some wide ranging assumptions (room widths 4m, roof angle 45 degrees, weight of half of each side of roof is directed down onto central support wall) there would be a load of 12.7kn acting on the lintel, increase by a 1.5 safety factor gives 19kn. Supremes info sheet gives a safe load of 20kn or 35kn for a140 x 100 lintel depending on orientation therefore appears OK, whether BC would use their experience/knowledge to accept or require calcs?

 

[^woody^]

I don't understand the relationship between the beam, stairs and doorway.

Any standard 1200 lintel wil do for any 1000 opening without calculation, unless there is a point load over the opening.

 

[Dereekoo]

I don't understand the relationship between the beam, stairs and doorway.

.

I think he is worried that if he goes ahead with any work through BC then BC will come back re none approval of existing steel beam?

 

[RScorpio]

Yes that's right, the existing beam is the big worry for me to proceed with any work.

 

[Dereekoo]

Any standard 1200 lintel wil do for any 1000 opening without calculation, unless there is a point load over the opening.

Which you may have with the struts coming down from the rafters

 

[^woody^]

Building control will only be interested in any existing beam if it impacts on the loading of the doorway or the stairs.

 

[RScorpio]

The beam is covered with wooden panels, so I will need to remove this to confirm but it seems likely that it is the 203 X 102 UB which has been added. Considering that it supports a slate covered roof which spans about 7.5m in total width, a solid plastered brick wall which is about 2.6m in height, ceiling on the 1st floor (again about 7.5m width) and flooring on the 1st floor (on one side only about 3.2m width), does it seem likely that it will meet the minimum requirements? The visible length of the beam is about 3.6m so am guessing it might be close to 4m in actual length including the supported hidden ends.

 

[Dereekoo]

Doing some very basic calcs with wide ranging assumptions on various loads gives bending moment values of 40knm for a 3.5m span and 50 knm for a 4m span
203 x 102 beam has a ultimate moment capacity of 64kn (S275 grade of steel assumed)
However taking buckling resistance moments moment values from standard tables (which will be conservative) for a 3.5m span and 4.0m span of beam gives 30knm and 26knm respectively.

So the size of beam is in the right ball park area (more so for the shorter span) but without detailed analysis nothing is definitive. It has of course stood the test of time and there are FoS included in any design and no doubt the roof has not been subjected to a snow loading of 75kg/m2 in these days of global warming.

 

[RScorpio]

Thanks all. I have tried to do my own crude calcs using examples which I could find on the internet.

Roof load -Fixed 1.41 variable 0.75 = 2.16kn/m2 X 7.5m/2 = 8.1kn/m.

First floor Floor and ceiling 1kn/m2 Fixed 1.75 kn/m2 variable= 2.75 kn/m2 X 3.2/2m = 4.4 kn/m

Masonry wall with plaster on both sides= 2.45 kn/m2 X 2.6 = 6.4 kn/m.

Total loading = 8.1 + 4.4 + 6.4 = 18.9 X 1.5 safety factor = 28.4 kn/m.

I think the safety factor for the fixed load is 1.35 rather than 1.5 so perhaps I might be ok for a 4m beam. Am trying to get hold of a structural engineer but so far am getting quotes of £800+ to do the calcs and provide a report which really seems excessive.

 

[^woody^]

Hang on. This beam has been up for all these years with no problems, so you are wasting time with amateur calculations trying to prove that the beam is or is not suitable on the basis that some inspector may or may not be interested in it?

If your council is anything like the ones I deal with around here, they accept certain beams in standard situations up to certain spans without calculations because they follow modern practices. e.g. 203 beams up to 4m spans are accepted

BTW, safety factors (indeed the actual end result) differ depending on whether you are following the old or new British Standard, or the Eurocodes