Stone Outbuilding Reroof - is this the right design?

[Lears]

Hi all,

 

I have a very tired, leaky outbuilding I'm looking to convert to an office. My understanding is I can reroof without planning permission as long as it's like for like given it's for repairs but could be subject to building control as it's more than 40% in one go...? More importantly though, I wanted to get some advice on how to reroof as I'd like to do this DIY if I can.

 

Ignore the dangerously low overhead cable, this should be gone by end of the month (fingers crossed!).

 

The existing rafters are way too thin and the ridge beam looks closer to a skirting board than a beam so rough plan was:

 

2x 47x220 c24 timbers screwed together as ridge beam (assuming this is total overkill but didn't want to take any risks - If I can get away with one, I will)

47x175 c24 rafters at 600mm centres

50x150 wall plate

40 or 60mm wood fibre sarking board above rafter and 175mm between rafter insulation

 

The rafters sit about flush with the top of the stone gable ends but hoping I can cut into it a little to get ladders over each end to give the gables some weather protection.

 

I've had a look at buying tailormade trusses ready to go but my assumption is nothing here will be straight or consistent so building by hand might be the better move.

 

Any suggestions would be greatly appreciated, especially if there's an easier way for an optimistic/ naive DIYer.

 

Thanks!

 

[Big Jimbo]

I'm no engineer, but aside from the double ridge beam (that i dont think would be required) I would imagine that roof would last well beyond your lifetime, and quite possibly that of your ancestors. What a great office that will make.

Edited September 8 by Big Jimbo

[Onoff]

Time might be better spent by shuttering and casting level wall plates down the long sides.

 

Then you could use trusses or it would make doing a cut roof easier.

 

2x 47x220 c24 timbers screwed together as ridge beam seems overkill thickness wise.