/ Construction advice.

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nocker - on 20 Jan 2014
I have an old timber conservatory which was created by enclosing the space between the back wall of the house and the kitchen and party wall. The original "wall" construction of the conservatory comprised two joiner made window units and a double door unit, tied together with the window units sitting on brick dwarf walls. Unfortunately the softwood units have started to rot and need replacing. I have been given a very nice set of aluminium double glazed sliding doors which I am wanting to fit. My problem is that the timber units supported the roof whereas the aluminium glazed unit will not do that. The roof is relatively light weight, comprising timber joists and polycarbonate sheet. One solution would be to insert a beam to support the joists/roof, but with a shallow fall on the roof I don't have much depth to play with. The span is 16ft and I would appreciate some advice on the necessary size of timber or steel beam / channel necessary to span this distance.
maisie on 20 Jan 2014
In reply to nocker:

You can always find sets of tables like this:

http://www.home-extension.co.uk/tech2.html

but they don't really apply to your specific situation. 16 feet is a massive span to cross, and your aluminium doors can't be that wide, surely. What's the minimum distance you can insert posts at - ie how wide are the doors when shut?

Have you also had a wee chat with the neighbour about the party wall? Putting in a timber frame might only require a framework which abuts the party wall, but an RSJ may need burying into the wall.

Martin
petenebo - on 20 Jan 2014
In reply to nocker:

can you reduce the height of the replacement units to accommodate the supporting beam?
nocker - on 20 Jan 2014
In reply to maisie:

Fair points Maisie and part of the reason I was asking. The aluminium door unit is actually 14ft wide and I was thinking to have a matching 2ft panel made to complete the enclosure. Each of the four glazed units which fit into the aluminium frame are 3ft6ins wide with the middle two being sliding doors. I had thought it might be necessary to insert some vertical supports but the visual impact would obviously detract from the potentialy very airy impression that could be created by avoiding that. I had thought of the party wall situation re an RSJ but we are on good terms with our neighbour or I considered constructing a corbel. Many thanks.
nocker - on 20 Jan 2014
In reply to petenebo:

Unfortunately not,the replacement units are four double glazed units which are virtually all glass, enclosed within a lightweight aluminium frame.
nocker - on 20 Jan 2014
In reply to petenebo: I was thinking to insrt a beam some short distance back from the glazed partition.

dyno-sore on 21 Jan 2014
In reply to nocker:

I suggest the following:

1. Commission the services of a structural engineer
2. Make an application for building regulations compliance

Unless you have a paper trail, you could have issues if you ever sell up.

When it comes to the weight (mass) of the roof; it's probably 'relatively' insignificant compared to the wind & snow loads which might occur.

Do it right; follow steps 1 & 2 above - it'll probably cost you less than a monkey. Which is perhaps what you'll feel like (or worse) if you get it wrong!

Also; if you are actually carrying out any work (at all) on the party wall; you will (legally) have to serve a party wall notice on your neighbour. You can serve this notice yourself or appoint a party wall surveyor; which might cost you 500.

I'm sorry, I can't give you the answer that you really want, but I offer the above advice for free!!
petenebo - on 25 Jan 2014
In reply to nocker:

Ah, of course. Sorry, misunderstood.

Setting it back from the partition seems to make sense but as Maisie says, it's too large a span to consider without additional post(s).

If you have to have a supporting frame why not make a feature of it with good quality, large section timbers, knee braces, pegged mortice/tenon joints?
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nocker - on 30 Jan 2014
In reply to petenebo:

Thanks for the ideas. For some time I had been thinking to erect a pergola type frame adjacent to the conservatory. It occurred to me to take this opportunity and tie the joists into it, making a feature of it as you suggest.

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