What kind of timber for load bearing bay window frame/posts

[paulbandler]

Hi,

This is not strictly a question related to 'period' properties per se, but I know there's a wealth of knowledge available from the regulars on this forum so I hope you don't mind this question.

I'm having an extension built that features a 'glazed bay' - almost a v. small conseratory attached to a kitchen. This bay has dwarf walls and timber windows all around to the roof level and glazed sections in the 'half-gables' of the bay's lean-to roof and 'Patent Glazing' in some of the roof. The timbers that frame the bay are exposed externally as are some of the rafters internally. The structural engineer's notes on the building regs application specifies the bay corner timber posts as 'C100' (or something similar - don't have it in front of me).

Now perhaps I should be getting this built by a specialist conservatory company, but I'm attempting to have it done by the general builder who is doing the rest of the work and want to use the same style of casement windows as having elsewhere (ie. non loadbearing timber window frame). The builder has told me that the timbers specified by the structural engineer are 'treated' and hava a 'rough' finish - like one expects on joists/rafters etc, and can't be readily planed smooth in a satisfactory way.

So my question is simply, what type of timber would one normally use to construct such a load-bearing frame for a glazed bay of timber windows?

Thanks in advance

 

[chuckey]

The "C" value is the strength of the wood, it is of importance when the beam is being used as a beam, i.e. trying to bend it. If it is used as column, the "C" value is of much lesser importance, unless you are going to load it to tons/square inch or its very tall and thin.
Go into your local (proper) woodyard and order PAR* (to the correct dimensions) and TANALISED. This is a vacuum impregnation of the wood with an anti-rot agent. Any proper timber yard will be able to supply what you want by sub-contracting out the machining. The other magic word is "clear", to you or me, that means without any blemishes, knot holes, shakes, bark etc, for timber on display.
So it goes "I would like X pieces of wood 3 7/8" X 4 1/2" X 47", PAR, clear and tanalised". It'll cost ya!!
For the beams, its the same but as they are not subject to the weather, but do carry a bending load. Is " X off 6" X 2" X 78" , C16, PAR, clear".
Building timber yards carry popular stock, hence the sawn, C16, tanalised 6" X 2" which your builder would use, because they are there.
Frank
On edit:- PAR= planed all round , nice and smooth(?)

 

[Penners]

PAR= planed all round, nice and smooth(?)

Sometimes called PSE (planed sides and edges).

Excellent clear advice there from Frank. Standard sizes of tanalised timber are invariably treated with just a sawn finish, so if they are then planed this removes part or all of the treated outer skin of timber. That's why this has to be a special order.

All I would add is don't leave it too close to the wire to order the special posts. Tanalith specialists will usually wait until they have a good batch of wood requiring treatment before they put it through. So you could have a bit of a wait for your timber. Order well in advance of your builder's need.

 

[paulbandler]

Many thanks guys - exactly what I needed!