Workshop Roof

topaz2008 · 17 Oct 2012

We have just had the blockwork completed on a workshop built from 100mm wide 7N concrete blocks. The gable ends have been built as well and the peak is 1m above the wall line. The workshop is 9m long and 5m wide. The joists will need to run across the 5m wall. We plan to put the roof on ourselves and after reading various websites we have some questions.

1. What size timbers do we fit on top of the wall to mount the joist on?
2. Do we fit a damp proof strip under these timbers?
3. Are these timbers screwed directly to the wall all are they floated on a bed of mortar?
4. What size timbers do we need to use to construct the roof frame assuming the roof will be fitted with concrete tiles.
5. how far apart should we fix the roof trusses?

Thanks in advance for your help.

noseall · 17 Oct 2012

Firstly, how can you build the gable before the roof structure is there?

You will maybe need to build-in a series of straps into the gable prior to building the gable end. The gable is then built using the rafter line as a guide.

....or if you build a cut roof you may need to build the purlins and ceiling binders in as well as the ridge board etc.

So, the question is: Are you building a cut roof or are you fitting pre-formed roof trusses?

All of the above will sit on a 75mm x 100mm timber wall plate bedded on mortar, directly to the top of the final course of masonry. This will be secured with holding-down bent straps. No need for dpc.

dannytylerwells · 17 Oct 2012

noseall";p="2545549 said:
Firstly, how can you build the gable before the roof structure is there?

its not unusual to build the gable first its not always ideal, but its certainly not a problem

first, lots of question which worry me as this is basic carpentry but its very important to get it spot on, perhaps u could ask a chippy who u know to come round and set out the first timber for u then that one becomes your template and away u go, or you could google the "birds mouth" cut then have a go urself with a scrap timber

i would use 8x2 timbers for the roof

4x2 for ur wall plate bed it down with cement, and i good idea to fix it through to the block work with 100mm frame fixings then put some wall straps along it

roof timbers 400mm apart

also dont forget your roof timbers will over hang your wall plate from the birds mouth this will form ur soffit/facia

hope this helps if i was closer i would come and show you for an hour so

please feel free to contact if you have any questions

noseall · 17 Oct 2012

dannytylerwells said:
its not unusual to build the gable first its not always ideal, but its certainly not a problem

It is a problem if he disrupts a good deal of masonry whilst chopping in purlins or straps to a rather fragile piece of masonry.

This is a forum where it is not necessary to use infuriating text speak. You are not charged extra for using whole words.

P.s. it is unusual to finish a gable before the roof is pitched. It is both pointless, arse about face and more labour intensive as well as dangerous in high winds to finish a gable before the roof is pitched.

Part built gables - yes.

dannytylerwells · 17 Oct 2012

hit a nerve there then

1m high gable, strong winds, there in essex not on snowdon, they come on here for advice, so give it! the gable is built so a solution needs to be found to work with what they have. simple its not a problem,

ps i will text/type however i like THK U!

topaz2008 · 17 Oct 2012

A bit more information:-

We had the brickwork and foundations done by a builder. He was supposed to finish the roof but kept messing us about. We have now sacked him and plan to finish the job ourselves. He built the gables first but they are slightly under the finished dimension so fitting the roof will not be a problem.

It will be a cut roof and not use pre-formed roof trusses.

Sorry to ask so many questions but these have arisen from reading different methods on the internet. I am aware of the birds mouth cut and how to work out the angles etc. My questions were really only about the timber sizes, spacing of joists and fixing of the wall plate.

noseall · 18 Oct 2012

You will need timbers in excess of 9" (225mm) for the floor joists probably spaced at 400mm c/c.

At 1m rise and a 5m span the roof comes in at roughly 22 degrees with a rafter length from top plumb down to plate beak of 2.7m.

The rafters are likely to be 150mm.

Some of the teccy guys with span tables may be along to give more accurate dim's.

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Workshop Roof

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