Building a flat roof for a garage

[williamglossop]

I have built the walls of my garage - its done in single skin 7N concrete block and is 4.1 meters long by 3.1 meters wide (couldn't make it any bigger). Its detached from the house, i.e. free standing.

I am now planning the roof and have never done one before.

I am going to span the roof joists width ways, i.e. 3.1 meters (plus overhang on each side for fascia boards). I am trying to work out what size joists i need.

The other thing is trying to decide the best way to secure them. Whats the most typical way of securing the joists? Hangers straight onto the top course or block? A wall plate all the way round then fix to that using straps?

I've tried google but cant find a definitive answer.

I am going to set the joists level and use firings from left to right to create the required fall.

 

[loply]

There are tables you can find somewhere with the standard joist sizes / spans for different grades of timber.

I'm not sure what you need to Google for, maybe something like "BRE timber span table"?

 

[geraldthehamster]

There are tables you can find somewhere with the standard joist sizes / spans for different grades of timber.

I'm not sure what you need to Google for, maybe something like "BRE timber span table"?

The tables are at the back of the old 1992 version of Approved Document A:

http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_1992.pdf

Cheers
Richard

 

[tony1851]

That's a handy link because, of course, the latest editions don't have them - TRADA want you to buy them instead!
(I've still got my tatty 1992 edition solely for the tables).

 

[catlad]

I would use 4x2" wall plates strapped down with 6x2" joists on top.

 

[williamglossop]

What's the best way to secure the joists to the wall plate? Will a 90 degree angled bracket on either side of the joist at both ends be adequate? Is there any reason why the joists can't be secured directly to the top course of blocks? Not sure what the purpose of the wall plate is.

Thanks again

 

[catlad]

The reason for a wall plate is to help attach your roof to your masonry using wall plate straps 3' long should be ample and to secure your joists just skew nail either side of joists with 4" nails.

 

[b21playa]

Fix wall plate using 3' restraint straps. 2nd pic in diagram below gives an example