cutting roofing timbers

[tommy d]

As per title can i cut my own roofing timbers for my own house or do i need to get them stress tested if so how do i go about this i know laws might be different in the uk but maybe someone might be able to help.

[codlasher]

Have you had any contact with a structural engineer? If so the specs on the timber sizes will be on your drawings.

As a rough guide a piece of 200mm x 50mm timber is able to span 4.0 metres. If this is a UK quality graded piece there will be either C16 or C24 stamped/inked upon its length somewhere. These C marks denote the structural quality of each piece. C24 being the better.

 

Rafters are normally 150mm x 50mm @ 400mm centres, but there comes a point where a purlin is needed or the size needs to go up to something of greater depth to cover the span required.

 

My advice will be to carefully go through the timber stacks at your local builders merchant and pick out all the pieces required marked with the C24 grading. This is what a structural engineer would ask to be put in your roof. Pick the best pieces too. When you use each piece make sure the curve faces upwards.

 

Are you birds-mouthing over the wall-plate? What pitch are you creating? Are purlins needed and from where are you picking up the supports for these? Have you thought about the insulation then the membrane and then the covering (tiles, slate, wriggly tin, etc)

Hope this helps.

codlasher

[farmerjohn]

as codlasher says get in touch with a structural engineer to design a roof structure if it is more complicated than a ridge to wall plate unsupported span of no more than what is specified for said timber size.

i always work on a 6x2 spanning 3.3m unsupported with slate covering. (thats mainly all we fit)

I would not bother buying C24 as at most merchants i know of they will stock both but C24 will be a lot more money.

regarding getting your sawn timber passed off as structural it all depends on the building inspector. I always have sawn, or saw my own oak beams out and visually grade them (making sure there are not large flaws in the beam) I have never been asked to produce a grading certificate for the timber (i think graded hardwood at mills around here are at least twice the cost of just sawn timber.) you'll get the same bit, just with a certificate.

it is a risk if you go down this route but i know my structural engineer and building inspector very well and i know to a certain extent what is a good structural piece of timber and what is not.

just to make clear, I do not tell the building inspector i have sawn the timber myself he just looks at the plan, looks at the timber and is away again. (they used to come and measure timber dimensions to see if they matched drawings when i first started off but dont bother now)

[OliB]

I'm going thru something similar at present, except where building regs specify 6x2 I'm using round log 8" top dia plus with one side flattened to fir roof board too, and notched to same thickness where it sits on wall plate. Building inspector has been notified, but yet to comment. At many times the mass, and only using clean logs without evidence of any structural defects I have my fingers and toes crossed that we will get the green light.

[tommy d]

Thanks for the replys I prob should state I live in Ireland and haven't looked into it too much just made a phone call today to the nsai (national standards of Ireland) to be told an engineer prob won't pass timber that is not stamped and if he did I could run into trouble if I decided to sell after I have access to Norway spruce and now I'm wondering how would I get it tested

[Woodworks]

Probably worth talking to your BCO they can be pretty helpful and knowledgeable. I know ours happened to be qualified to grade timber as I used ungraded timber for our roof.

[codlasher]

Someone is taking the p*ss charging more for C24 over C16! In my experience they are often mixed in the same pack. If you want a specified amount/lengths just ask.(I may be lucky and just have a very good merchant nearby?)

 

I do know that the Irish building regulation requirements are slightly higher than those in the UK. This is perhaps to ensure that any construction is able to cope with the more extreme Irish weather.......I do know that the Irish insulation 'overlaps' at floor and roof levels require more care/attention. This is not difficult to achieve but takes a little longer.

I think you have made the right decision to call the standards office. Don't forget the building inspector is there, too, to help and advise. Folk forget this! It it the 'planners' who are the difficut ones..........

I can't help with Irish grading marks but I would suggest researching this too.

What has been forgotten is treatment against insect attack. White untreated timber is like spreading out a picnic for these and I would strongly advise against its use. One dodgy wood-worm infested load of firewood will see your hard work reduced to a mess in a decade!!!!!

The best roof timbers are wrc (Thuja) then Scandinavian pine followed by European larch if you can get this. I'd avoid Norway spruce if at all possible. Sitca spruce is ok but it should be stress graded......So you are back to square one!

 

Finally, don't forget to VENTILATE! ooh-er Doctor:laugh1:

codlasher

Edited June 3, 2015 by codlasher

[OliB]

Another thing to consider is getting certified to grade timber. I am currently looking at this.

 

In England its a different system for hard and soft wood. Softwood grading costs over £1200 from quotes I've had, but hardwood between £500 and £800. All hardwood with moisture content over 20% or any dimensions over 2" or 4" (cant remember which off top of my head) is graded as green. But if you offset the cost if this against being able to grade timber for your own use and what you can sell on it's worth it.

 

I've downloaded the trada handbook on grading hardwood, and it's nothing that someone used to milling, or working with timber would find difficult.

[agg221]

All hardwood with moisture content over 20% or any dimensions over 2" or 4" (cant remember which off top of my head) is graded as green. But if you offset the cost if this against being able to grade timber for your own use and what you can sell on it's worth it.

 

I've downloaded the trada handbook on grading hardwood, and it's nothing that someone used to milling, or working with timber would find difficult.

 

Just to clarify.

 

Softwood is mechanically graded, hardwood is visually graded. There is technically no grading standard for green timber (mc >20%). This is an oversight, but it means that if you install green hardwood you are not actually obliged to pass any grading standard.

 

In practice, common sense dictates that it is a good idea to make sure that it would pass visual grading (by reference to the standards as per TRADA publication) but you do not need to either be qualified or have it done by someone who is.

 

One caveat, this was the case 3yrs ago when I did it, but I have not checked whether this has been updated since.

 

Alec