New garage roof

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Hi, I'm building my own detached garage to the front of my property.

I'm up to the roof now (which is going to be hipped), I've bedded the wall plate in, installed joists and OSB so I can walk about to construct the roof and ready to cut the rafters and ridge.

I'm having an 8:12 slope, finished in concrete tiles. Span is 3.1m, length 5.9m. Dry ridge and hip kits

My questions:

1) Do I calculate the ridge length by halving the long length and deducting it from the overall length? Or (half the side wall x 2) deducted from the long wall (I've seen both mentioned so not sure which to use, I know there's not much difference in my case, I just want to get it right)

2) Are there standard overhang sizes in order to make facia/soffit/gutter installation easier

3) Will I need ventilation other than soffit vents and the dry ridge kit (which allows ventilation) if the roof isn't insulated?


Thanks in advance,

Mike
 
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The inverse tangent of 8 divided by 12 is 33 degrees. MY brain only works in degrees, lol.

1) The ridge board will be short of each side wall by half of the width of the extension. So if your hipping it left and right, your ridge board is in effect 5.9m minus 3.1m = 2.8m

2) you can have sofits and fascias as big as you want. Fascia standard is 150mm.

3) You don't need sofit vents. The breathable roofing felt and dry ridge is sufficient. Insulation is only a problem if you insulate between all the rafters under the felt if the room is not being heated and used. It just causes condensation. If you're concerned about airflow, with over facia vents on the top edge of the fascia before tiling. Use it as the break lath.
 
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Thank you for your reply!

So would a 100 or 150mm (level) overhang be sufficient? With 150mm wide fascia.

And do I need anything Unger the felt at the bottom? I've seen felt support trays and things for ventilation, I'm not sure what I'll need and what is optional.

Cheers,
Mike
 
Thank you for your reply!

So would a 100 or 150mm (level) overhang be sufficient? With 150mm wide fascia.

And do I need anything under the felt at the bottom? I've seen felt support trays and things for ventilation, I'm not sure what I'll need and what is optional.

Cheers,
Mike

Size of soffit is personal choice, just what looks good to you. The bottom of the felt can often perish so you can fit eaves felt trays, they're 1.5m long. I've seen people butt them up to one another and other people overlap them when fitting. Found at builders merchants and places like Eurocell.

https://www.roofingmegastore.co.uk/...tm_term=4575480200600063&utm_content=Shopping

If you're concerned about ventilation, put over facia vents on top of the fascia before tiling.

https://www.screwfix.com/p/over-fas...nQ&gclsrc=ds&dclid=CLzll7ivsN0CFVe3GwodF6oNgA
 
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Thank you for your help, much appreciated... I decided to go for 100mm as it's only a small building. I have attached a photo of my progress so far.
 

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Cheers Andy, that did cross my mind but my original plan was to have loft space for storage... after checking the plans I realised I'm not going to have as much as I'd hoped but will leave both sides boarded out and the middle for access
 

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