New lean-to roof

wadge · Posted: Thu Apr 03, 2008 8:11 am Post Subject: New lean-to roof

Hi, I'm building a single skin (with thermal panels to meet regs), single storey extension and need some help regarding the roofing.

1. How does the wall plate at the lower end of the roof need to be attached to the single skin block work? I read of bedding it on mortar, strapping it, screwing it and using anchor fastners?

2. On the ridge side of the wall, can I use joist hangers or is a continuous ridge plate the preferred option?

3. Are the rafters notched at both ends so they sit flat on the wall plate and joist hanger/ridge plate?

Overall dimensions are 2.1m * 5m

noseall · Posted: Thu Apr 03, 2008 6:41 pm Post Subject: Re: New lean-to roof

[quote="wadge";p="871352"

Quote:

Hi I'm building a single skin (with thermal panels to meet regs), single storey extension and need some help regarding the roofing.

why bother with single skin. by the time you have added the insulation to the inside then you are almost at the same thickness.

Quote:

1. How does the wall plate at the lower end of the roof need to be attached to the single skin block work? I read of bedding it on mortar, strapping it, screwing it and using anchor fastners?

bedded on mortar and strapped down using galvanized bent straps.

Quote:

2. On the ridge side of the wall, can I use joist hangers or is a continuous ridge plate the preferred option?

use a continuous pole or pitching plate that is bolted to the wall.

Quote:

3. Are the rafters notched at both ends so they sit flat on the wall plate and joist hanger/ridge plate?

at the top the rafter end is cut to the pitch, meaning it will sit flush against the plate. at the bottom end it will be birdsmouthed onto the wall plate.
[/quote]

wadge · Posted: Fri Apr 04, 2008 9:10 am Post Subject:

Thanks Noseall.

It's single skin because the overall width is 2.1m so every inch is precious. If I was to build it using a 12" cavity wall I'd lose too much space. Single skin and boards means the overall thickness of the wall is:

(20mm render) + 100mm block + 50mm battens + 50mm Celotex = 200mm excluding the rendering compared to 300mm for a cavity wall.

I would have thought that sitting the rafters on joist hangers at the ridge end would be stronger/easier. Any reason why that can't be done?

noseall · Posted: Fri Apr 04, 2008 4:50 pm Post Subject:

because it is more difficult than my suggestion.

you cannot get 'pitched' joist hangers.

wadge · Posted: Fri Apr 04, 2008 5:17 pm Post Subject:

The plan was to cut out an 'inverse' birds mouth in the rafter so it sits square on the hanger.

noseall · Posted: Fri Apr 04, 2008 5:26 pm Post Subject:

it will take a few minutes to bolt the pitching plate to the wall, then each rafter can be spiked to it. why do you want to waste time with hangers as well?

so long as the (lower)wall plate is strapped and anchored, the roof cannot drop.

unless you think the wall will push in.

by the way, a pole plate/pitching plate/bearer plate can be fixed directly below the rafter ends also, so they rest on top of the plate:wink:

wadge · Posted: Wed May 14, 2008 10:00 pm Post Subject:

Thanks for the advice. Got the roof up today.