roof joist spacing

[blackrodd]

What's do you mean problems start at 35 degrees Rod? What for?

Yeah I think I may go for 2x8s bill. Could be better PFF with that really.

Roof angles, after 35 degrees and lower, some tiles won't work, so you end up with loads of variations in lap (batten) spacing, double layers of tyvec, or similar, all designed to get the water off quickly and stop water ingress by snow, wind etc.
Regards Rodders

 

[RogerBoyle]

Have a search on http://www.diynot.com/forums for the amount of people that have had problems with low pitch extensions and roofs

then get as much pitch as you can to eliminate the potential for problems

Roger

 

[markblue777]

Hi all thought a picture of the proposed extension may clear a few things up.
I may just be working it out wrong and the pitch im saying is wrong but using the protractor in sketchup shows 20 degrees so thats why i believe it is a 20 degree pitch.


Cheers
Mark

 

[RogerBoyle]

by going closer to the window and notching over the wall plate you will gain a few more degrees
Regardless make sure that the guy you get to do the work has plenty of experience in building low pitch roofs. And has contact details of past customers that have had low pitch roofs.. You should also be aware that there are different flashing kits for the Velux windows which one you get is dependant on your Pitch.

You must check the tile specs from the manufacturer

if you have a pitch of 20 degrees do you really want to use a tile that is only rated to 18 degrees or would you rather have a tile rated to 15 degrees do not believe anyone else when they tell you what rating the tile has other than the manufacturer. Call them LOL

Roger

 

[markblue777]

Hi Roger,
The only trouble is if I increase the pitch to 30 degrees the lower end of the wall ends up as about 5ft 8 inches (to small).

With the pitch at 25 degrees the lower end of the wall ends up at about 6ft 10 inches
with it at 20 degrees the lower end of the wall ends up at about 7 ft 8 inches.

The floor thickness i am saying is 150mm would that be about right or should it be more or less for a concrete slab? as that will obviously dictate how much room i have from the floor to the ceiling as well

Cheers
Mark

 

[=Adam=]

Hi Mark,

My day job is structural engineering, I do calcs like this on a daily basis.

Please feel free to pm me some more details about the project and I will knock up some calcs to prove the joist dimensions and spacings.

Thanks

 

[blackrodd]

You're finished floor inside, will be the same as the dpc, which will be 6" min. above outside the path.
You should be able to see this dpc between the bricks or it will be at the bell cast bead level if you're house is rendered.
Any raised wooden floors inside will be above dpc usually.
So it won't be easy to lower the floor level below existing dpc.
Regards Rodders

 

[RobinBHM]

A more attractive solution maybe a flat roof with a glazed lantern. I tend to think low pitch tiled roofs can look unattractive. Restrictions caused by low 1st floor windows and / or planning has made shallow pitches more commonplace these days, but they often look a poor compromise. Careful detailing is important when using tiles at their minimum pitch to avoid risk of leaks.

A flat roof with a mansard perimeter pitch is also an alternative option.

 

[RogerBoyle]

Mark
are you doing the work yourself or are you getting a builder in to do it
Re the floor.
You can have the floor lowered but that can cost silly money both in materials and labour and can often times open up another can of worms lol

Agree with the post by Blackrodd

and at the pitch you are looking at I Personally would go with something along the lines of what RobinBHM suggests and although care still needs to be taken they are easier to get water tight than a low pitch roof

And Pm =Adam= for the calcs

 

[markblue777]

Hi all,
Ah OK so the 150mm I was saying for the floor is right. (I don't want to lower the floor I just did not know 150mm was correct)

The mansard perimeter pitch could be a solution. Need to talk the the misses and see if she likes it.

A building will be doing the the build to the point of make it water tight then I will do all the inside.

I just want to get a design down so I can take it to show and work off so I can get more acuate quotes etc.

Adam I will PM you shortly.

Thanks for the info everyone. Its a great help to understand it all and possibly save me money in the long run by designing a roof that is right. And still looks OK to the misses standard haha.

Mark

 

[lincs1963]

If these spars are also forming your ceiling you won't be needing the bracing. 600 centres with double spars either side of the windows is suitable for this application. There is no real need to put ceiling ties in, so leaving a sloping ceiling giving extra height and making the room feel more open. At the pitch angle you are working to there will be very little outward pressure on the wallplate. HTH, Neil.

 

[markblue777]

A more attractive solution maybe a flat roof with a glazed lantern. I tend to think low pitch tiled roofs can look unattractive. Restrictions caused by low 1st floor windows and / or planning has made shallow pitches more commonplace these days, but they often look a poor compromise. Careful detailing is important when using tiles at their minimum pitch to avoid risk of leaks.

A flat roof with a mansard perimeter pitch is also an alternative option.

Hi Robin,
Am I correct in saying that you can still have vaulted ceilings with the mansard perimeter pitched roof. From a quick google it seems possible. Is there a max span that it can go over? The span for mine would be about 2.6 meters (so possible beef up the joists to a 2 by 8 or more)

http://www.seamlessroofing.co.uk/mansardvaulted.html

Cheers
Mark