Loft conversion steel installation.

[robmorphet]

(This referrs to a previous subject)

Given that I've asked 4 builders for quotes, two turned up and still haven't bothered to quote, or even give me an idea of price, so blx to them, I'm doing it myslef. I am going to use the building regs too. \Its too complicted and too much of a gamble!

I'm getting the steel sizes from a surveyor, anyone any refs to suppliers - could i use reclamation yards? or is it better to buy new?

I'd quite fancy using those pre-formed (rolled sheet steel ones) (mates just removed a supporting wall and used one, apparently 60% lighter than normal I RSJs.

Any help would be appreciated.

many thanks
rob.

 

[kostello]

use the size that the engineer says.
reclamation yards are fine for steels.
its good to get them cut to length as it really needs a grinder or welding torch

aleks

 

[masona]

You can get the welder to make a joining connection which slide the two RSJs together with nuts & bolts.This will make it lighter to carry around and manoeuvre into position.

 

[robmorphet]

thanks guys.

found a website that quotes for new steels - Parkers-Steel.co.uk which is good as they have loads of different sizes and legnths etc.

Two questions (sorry)

1. runs are 7.5m! Thus they will be split. To join over a supporting wall(below) do the ends meet face to face, ie I to I and then a plate is bolted on the web, or, do you face off each end with a piece of flat drilled so your bolting two flats togther. I'm doing it myself (have welder and grinder and connon sense!)

2. Also, I'm spanning 7m with wood. Does anyone know how to calc the joist size please? ie the depth, width and joist ctrs. Appreciate the advice.

Cheers
Rob

 

[amtodd]

Before I post a small essay on this subject, are the joists for a ceiling only, floor and ceiling, floor only, flat roof with access, flat roof with maintenance only access? Oh, domestic, commercial or industrial?

 

[robmorphet]

heres the deal:

Its a loft conversion residentail.
One side of the bungalow (new extension)has already been converted so the stairs are in.

The other side (org/existing) is just a loft.

We'vbe got PP for the conversion. its 7m wide by 9m deep and 2.5m high. its got full heiht gables at both ends.

There will be two small hipped roof dormer windows in the back and two velux type at the front.

The existing "floor" is the celing joists, suspended by trusses in the shape of a V on an angle.

There will be 5 steels going in. 1 at the highest point and two at about 3' off new floor level to support the roof when the trusses are removed. these roof steels can be supported at 0m, 3m and 7.5m by a supporting wall downstairs - hence the join.

You can see pics on my web site here: http://www.morphet.co.uk/house/may_1/index.htm (hope that okay!)

Two more larger steels will be installed for the new floor joists, which will sit in between the existing (downstairs) celing joists. - span of these 7.5m max.

Does that help!

really apprecite the advise given and understand that there's no legal comeback - I just need an idea of how to do it!!

cheers guys
rob.

 

[amtodd]

Hi Rob,

Having seen your site, looks like you have sufficient head room to put a steel or two in as trimmers (ie down the middle of the span), effectively cutting the span of the joists to around 3.8 meters and therefor bringing them down to off the shelf at Q&B sizes.

If you don't want RSJs runing lengthwise down the middle of the house here are some thoughts.......

The largest timber stated in the regulation span tables is a 75 x 220, which at 400mm spacing and using SC4 timber (what is usually supplied unless you say otherwise will be SC3 at best) will span 5.25 meters for a domestic floor /ceiling, 5.42 meters for just a floor.

This doesn't mean you can't use larger timbers or spans, but if you do, you will have to show the local control office your calculations as they can't just look them up either.

I would take a trip to the local library - better still local college / uni library if they have any civil & building engineering courses, many don't check who references books, just borrowers - or consult an architect who for his / her fee could also sort out builders.

However......
As a rough guide doubling the height of a beam in any material should double the permissable span.
Making the beam taller and longer makes it prone to twisting and rotating especially with timber, so you will need to increase the width to stop that.
Making the joist wider makes it less likely to twist as it gets taller / longer, but only adds a small mount to the span, as most of the gain in strength is taken by the increase in weight of the beam itself.
Above 5 meters in length or 250mm the cost will soar, as obtaining a suitable timber will become more difficult.
Back of a fag packet guestimate suggests SC4 97mm x 300mm would do the job.
These will cost a small fortune, but they are obtainable from specialist suppliers.

Of course the beams will weigh a significant amount before you even introduce a load, so the supporting walls etc might need to be reinforced in a suitable fashion to accept the weight, and this will need calculations.

You will therefor have to research this out properly, and should not accept my guesstimate as accurate.

 

[robmorphet]

so,

If i introduce steels at intervals into each supporting wall the timber used can be reduced also? Does your data show what size I can use? I think spanning the 7+m is too much (distance and weight) and if I increase the depth of the timber the floor level will rise anyway (which is why I thought about the big span in the first place.)

so,

rather than 2 floor steels I place in 3 - what size joists would I need?

Also, do you know about the joining method? Do I cap each RSJ off with a face plate, or can I bolt a joint strip on the web?

Thanks very much for your help amtodd, its very much appreciated.

 

[amtodd]

rob,

Sorry, nothing to hand, no knowledge of figures, only the general principles. Have always had an architect risk their insurance calculating metal works. They supply dimensions, steel grade and jointing instructions.

With steel in general, manufacturers specify max load per linear unit per size per span, (The tables are on the web) which means you need to know what load you are carrying and calculate backwards.

To get the load you'll need to calculate the weight of all timber joists supported by the steels, and add about 0.5kN/m sq for the floor and ceiling components (floor boards, plaster board, skim , cabling etc.) Then divide back.

Good luck.

 

[kostello]

it might be worth your while going for enginnered timber beams.
have a look at www.howart-timber.co.uk

i have used i joists from them a couple of times.

you send them the drawings and they stick it all in the computer and come up with a solution to building regs.

they will also be able to size timber beams to go in place of the steels if you are interested.

enginerred timber is about 2.5 times stronger than rerlar timber and doesn't shrink or twist.


i'm also sure that they will have a joist for your span

aleks

 

[robmorphet]

Cheers Kostello.

I cant link to the site though - I'll do a few serches on the web.
I'm based in manchester NWEng, so a local firm would be ideal.

Thanks guys for your help, I'll post another soon no-doubt!!

Cheers

 

[kostello]

it doesn't help that i can't spell

try www.howarth-timber.co.uk

they supply nationwide

aleks

 

[robmorphet]

thanks Kostello, they have bases about 5 miles away - superb mate.

(ps google found the link for me too!)

rob