few newbie questions

[grahama]

Hi all,

have been getting some great advice in the building section so here I am in roofing section for some more !!

Ok, am new to roofing as I was to building so here goes.

I am putting a vaulted roof on my single story extension. A structural engineer is calculating the ridge beam for me as building control want some done, and I understand that I need common rafters at 400 centres.

My questions are...

does the first rafter attach to the wall of the existing house ??

what type of membrane goes under the battens, waterproof or semi permeable??

and do I put some sort of board under the first tile at bottom of roof??

Will be back for more info I'm sure,

Graham

ps, and articles I can look at will be great.

 

[pinenot]

In stating - a vaulted roof - you are describing an arched roof structure, fairly ambitious for your first roof, if I'm catching you right!...pinenot

 

[tony1851]

In stating - a vaulted roof - you are describing an arched roof structure, fairly ambitious for your first roof, if I'm catching you right!...pinenot

 

[^woody^]

No
Any
Yes

LOL , Oh Pinenot

 

[grahama]

Ok, might be describing it wrong

I am doing a single story extension to replace a conservatory, but the roof has a gable end

something like this, very rough I know !! (red id existing house wall)



Inside I am not putting a traditional ceiling in but want the roof to be seen up to the roof windows, like a loft.

I have just got the calcs back from the engineer and need two bolted together 75 x 225 beams for the ridge beam which is fine as it makes the fitting of battens easier.

So, my existing questions still stand if u can answer them

My questions are...

does the first rafter attach to the wall of the existing house ??

what type of membrane goes under the battens, waterproof or semi permeable??

and do I put some sort of board, ( eaves membrane protector), under the first tile at bottom of roof??

Hope this makes things clearer.

Graham

 

[grahama]

Sorry Woody,

just got in from meal and pub and took me a while to get your post lol.

Where does the first rafter position then??

 

[tony1851]

calcs back from the engineer and need two bolted together 75 x 225 beams for the ridge beam

SE over the top again as usual, eh Woody?

first rafter does not get fixed to the house wall, just an inch or so off it. Membrane = breather membrane; just drape it under the lower tile and into the gutter.

 

[grahama]

Thanks Tony for that, just what I wanted.

As for the structural eng, apparently it was touch and go if I was going to have to get a steel for the job

I am getting brickwork done by a builder friend as I can't do that tbh, and he said he is seeing more and more over engineered specs for things like this.

Thanks again everyone,

Graham

 

[tony1851]

As for the structural eng, apparently it was touch and go if I was going to have to get a steel for the job

As a matter of interest, what is the span of the beam (ie clear distance between house wall and inner wall of new extension), and the internal width (side-to-side) of the extension?

 

[grahama]

outwards as you described it is 4M, side to side it is, (where the wall plate sits on inner block skin each side), 4.2M.

What are your thoughts, I am using Marley Modern concrete tiles as per the house, all of which was on plans to SE.

 

[tony1851]

The main criteria for the ridge beam will be checking 1. the bending stress in the beam and 2. the maximum deflection (sag) under maximum load.

In this case, deflection will almost certainly be the critical aspect, and considering the span, IMO the SE has got it about right.

If it works out cheaper, a single 12" x 3" or 12" x 4" would be equivalent (though they would stick down a bit).

 

[freddiemercurystwin]

Isn't that one of your drawings tony?

 

[tony1851]

Isn't that one of your drawings tony?

No, I'm afraid they're not that good

 

[grahama]

Nice to have the calcs I have paid for confirmed. Will stick to the engineer's recommendation wood wise as that is what will be submitted to building regs dept. 75 x 225 C24's aren't that expensive in 4M lengths, about £25 each.

May I ask Tony where you have got your knowledge from, (not knocking your skills btw) just wondering how easy these calcs are and whether you are a SE too ??

If my SE has got this right then it gives me confidence in the steel he has done calcs for, which, when I open up the livingroom wall will be holding the back of the house up.

 

[tony1851]

What is the span of the opening, and what size steel(s) has he specified?