Removing Purlin Supports / Struts

[jagillham]

Hi all,

I'm looking to remove the diagonal struts in the loft as part of a "half-conversion".

I did some time ago instruct a SE to do the calculations for this alongside some other works about a year ago. I'm now in a position to start, so have started to look at these in detail.

The property is a 1903 terrace, with one purlin on each side supported by a diagonal strut. The support and purlin themselves are "2 by 4".

The SE has specified a C24 250mm x 100mm timber, which seems huge to the point I'm struggling to find somewhere that has them. I also have no idea how such a timber would get into the loft. Had I noticed this at the time I would have probably asked for an RSJ that could be assembled in the loft.

Does the specified timber seem excessive, or is that fairly standard? If I was going down the RSJ route, I assume a smaller sized steel would be required?

Any thoughts welcome.

Excuse the mess, everything has been thrown up in the loft whilst rest of the house was being done!

 

[tony1851]

A 250x100 does appear at first glance excessive for that span, though it is probably deflection that is the governing factor, hence the deep beam.

But, yes, the SE doesn't seem to have explained (or perhaps care?) how you would get such a big beam up there, and this is where theory and practice diverge.

If using steel, a section such as 152x89 would suffice, and you could arrange to have flange- and web plates cut and drilled to form a bolted splice connection. In two halves, that would be much easier to get into the loft, but it would probably be more expensive than the timber beam.

 

[freddiemercurystwin]

"half-conversion"

/shudders

 

[tony1851]

Maybe he just wants to beef the floor up for storage?

 

[jagillham]

Yeh I knew there would be some murmurings about that. The upshot is that firstly due to the open plan ground floor there is literally no way of being "building regs compliant". The kitchen is open plan to the lounge and the exits are on the opposite side to the stairs. Secondly we have no intention of selling, it's a cheap house we making the best of.

I have coupled the existing joists with C16 45mm X 145mm timbers already. We have a whole house wired smoke alarm system and will be using fire doors etc. There are millions of 3+ storey 'turn of the century' properties in this country nobody would think twice about buying without protected means of escape etc. /rant.

I'm fairly confident it was the same SE who specified a 203 X 203 beam when the upstairs wall was taken out. Nothing sits on that beam except the loft floor. Builders seemed to think this again was overkill.

 

[jagillham]

Any idea on the cost of the spliced beam? The whole ones down stairs were about £100 each, which in the grand scheme of things is pocket money compared to what was spent on plasterboard or screws or carpet or whatever!

 

[jagillham]

I'm back onto this for the summer

Can anybody confirm the most suitable RSJ, I have a little more information now...

Span: 3.900 m
Dead load: 1.72 kN/m
Imposed load: 0.87kN/m

Tried looking for some online calculators, but could not find one I can put the above in for an answer.

 

[freddiemercurystwin]

You'll need an SE to do the calcs to pass on to BC anyway. Prolly a 203 or sumink.

 

[jagillham]

I'm more worried about "safe" than "BC passed" at this stage. As mentioned in the original posts complying with current regulations is simply impossible given the current layout / situation.

I have all the calculations from the SE here, just they have specified a timber beam that is never going to get into a mid terraced house. I was hoping a spliced steel beam would be more practical and not be as tall (as this beam will intrude on the headroom above the stairs).

Maybe naively, but I was hoping I could simply find a table online that showed a steel beam that met the already calculated loads.

 

[RonnyRaygun]

The size of the beam is one thing, and you might get someone to confirm a size for you, but you will still need to get the splice designed by an engineer, as no-one on this site is going to be willing / able to do it for you.
And you will need your masonry checked to determine pad stone sizes.

 

[jagillham]

I have the specs for the padstones too from the original SE.

Is there not some chart or conversion where I can find the equivalent steel to the spec'd timber beam? Or where I can put all the calculations in I have already?

All the hard work in terms of all the loads has been calculated already, I simply need to convert that to a steel that fits the description.

 

[RonnyRaygun]

I can't see what you gain from sizing a beam using a table when your issue is getting the beam into the loft, hence the need for the splice. The splice is the more complicated part of the design and you will need an engineer for that anyway.
If you instruct an engineer to design a splice they will want to size the beam as well.

Although, Tony has given you a steel size above which will be "safe".

 

[RonnyRaygun]

deleted

 

[freddiemercurystwin]

You can lead a horse to water .....