Cut roof - a couple of queries

Hello, I'm just about up to roof level on my extension and could do with some advice please.

It's a duo pitch cut roof that will form an attic style bedroom. The rafters are 7.2M long and 175mm x 50mm at 400 centres (SE's specification). Support is provided by the outer walls, a steel ridge beam with bolted on wall plate and an intermediate purlin each side. All rafters will be birdsmouthed and secured to the wallplates with truss clips or framing anchors.

My questions are -------

1) Will I have to fit the full length rafters or can I fit two half length rafters and overlap them on the intermediate purlins?

2)Will I need to fit any bracing? All the stuff I've read seems to apply to trussed roofs but it's not clear if it also applies to a cut roof.

Any thoughts would be appreciated.

if you have a mid-span purlin then it sounds as if it has been designed with a split rafter in mind, i.e. two pieces.

bracing will apply and should be specified. bracing usually occurs every 2m.

why truss clips?

nail, screw or paslode. truss clips are flimsy and will be undersized in my opinion.

you can't beat a good 4" nail-or-three skewed into the b/m connections.

by a cut roof one can assume you mean traditional.?

you can join the rafters overlapping on the purlings you would normally bolt them together with star washers. giving a decent overlap.

with regard to bracing the bracing you refer to is normally for truss roofs in a lot of cases ply wood is used on the under side for bracing for this type of roof. it should show on your plans from SE the construction of the roof and any structual bracing where required. also if you are putting in any type of windows you will probably be required to double up the rafters either side of openings bolted together.

before doing any thing run your ideas by your local building inspector he will be more than happy to advise you .

without seeing the drawings its difficult to picture the job in its entirety
but hopefully this will help.

noseall said:

bracing will apply and should be specified. bracing usually occurs every 2m.

Click to expand...

sorry for the confusion, i will clarify:

by bracing i was referring to strapping, i.e holding-down, across joists and across rafters.

there is not the need for 4" x 1" bracing.

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why truss clips?

we have one arcitect that will not allow any thing other than clips even on traditional construction. on his projects


WE just smile and take his money.

Thanks very much for your thoughts. Using the shorter rafters will be a big help to me.

I've probably used the wrong terminology, I should call it a traditional roof. For information there is one dormer window which is a strange triangular shape and the SE has specified a double rafter to accomodate it.

The SE's spec was supposed to be comprehensive, it includes the size/position of purlins/rafters and the size/position of anchor straps and lateral restraint straps. It says all rafters to be birdsmouthed over wall plates and secured by nailing or proprietery galvanised fixings. It makes no mention of bracing. From what you've said it sounds like it isn't an ommission as there isn't usually any bracing for this type of roof only strapping which has already been specified.


Thanks for your advise about truss clips, as an amateur I thought it would be easier for me to hold the position of the rafter using them rather than skew nailing but I'll think again.

What about framing anchors instead? and what is 'pasload'?

Any additional comments would be welcome.

pasload - automatic nail gun.

O.K. Thanks a lot for the advice it's been very helpful as always.

pasload one of the best tools we ever bought.