Cut roof instead of trusses

Ive a garage roof that ill be doing at my place in a few weeks. I was originally going to install attic trusses but with the cost of materials going through the roof, im now considering doing a cut roof instead.

My garage is 11m length x 8m width. The attic trusses where going to be 9x2s all over whereaa my cut roof will be 9x2 joists snd 6x2 rafters. A 9x3(or4) purlins.

The attic trusses or cut roof will be resting on a wallplate both sides and sitting on an 8x4 (or 8x8) rsj along the centre length.

The trusses where going to be spaced 600mm centers. Any cut roof ive worked on has been 400 or 450 centers. Looking online i can see cut roofs can be spaced 600 centers also, however can i still use 6x2s for tge rafters or would i need to use something bigger than this? Im at the pricing materials just now to see the difference in savings.

Labor is free with son and uncle giving a helping hand.

2020c said:

Ive a garage roof that ill be doing at my place in a few weeks. I was originally going to install attic trusses but with the cost of materials going through the roof, im now considering doing a cut roof instead.

My garage is 11m length x 8m width. The attic trusses where going to be 9x2s all over whereaa my cut roof will be 9x2 joists snd 6x2 rafters. A 9x3(or4) purlins.

The attic trusses or cut roof will be resting on a wallplate both sides and sitting on an 8x4 (or 8x8) rsj along the centre length.

The trusses where going to be spaced 600mm centers. Any cut roof ive worked on has been 400 or 450 centers. Looking online i can see cut roofs can be spaced 600 centers also, however can i still use 6x2s for tge rafters or would i need to use something bigger than this? Im at the pricing materials just now to see the difference in savings.

Labor is free with son and uncle giving a helping hand.

Click to expand...

I doubt you'd be able to cut a roof and fix it for less than trusses, but who am I to argue.

Your rafter/joist spacings need to be worked out based upon your structural timber sizes and loadings. FWIW we NEVER space at 600mm if we can avoid it, even with trusses. But this is a personal (roof battens breaking) thing of mine. It sounds to me like you are just guessing your timber section requirements rather than engineering them.

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More info required: I assume you want to use the roof space fully if you're looking at attic trusses? How steep is roof? Rafter size requirement is affected by angle as well as length.

I would expect attic trusses to span 8m without central support but they will likely need a crane to install. Generally trusses will use less timber than cut and pitched simply because the individual members are working more efficiently. Also there is a lot less time and skill required in placing them


This needs engineering not guessing.

noseall said:

I doubt you'd be able to cut a roof and fix it for less than trusses, but who am I to argue.

Your rafter/joist spacings need to be worked out based upon your structural timber sizes and loadings. FWIW we NEVER space at 600mm if we can avoid it, even with trusses. But this is a personal (roof battens breaking) thing of mine. It sounds to me like you are just guessing your timber section requirements rather than engineering them.

Click to expand...

19 trusses are coming in at 240£ or 250euro a truss and thats without the bracing. which is 4560£ or 4750euro. And bear in mind if im to install any roof windows more that the spacing between the trusses, ill need to double up the trusses at each side of the windows. thatll be another 4 trusses if 2 windows go in.

the cut roof materials are coming in at 1850e euro. Thats for 600m centers.
6x2s 6m 45 off for rafters
9x2s 4.2m 38 off for joists
9x2 6.6m 2 off for ridge board
4x2 2.4m 19 off for collars
9x2 4.8m 4 off for purlin
4x2 4.8m 9 off for under purlin.

Labor for both are free. Plus ill need a teleporter for errecting the trusses. building the cut roof, i have my own scaffolding and trestles, boards etc..

As for the nails, wall plate, straps etc.., ill need them for either trusses or cut roof so no need to price up here.

My own house trusses are spaced at 600mm which we installed 25 years ago. roof tiles and never any issues with snow loads or high winds.

Ill be installing flat roof tiles again on the garage.