Snow loading and roof supporting posts.

[Deluks]

Have asked this question before in a long winded manner, with several links to other posts, which just confused the issue, so I'll try to keep this as brief as I can and hopefully any answers will be the same

The wall in the pic consists of 3x3 posts concreted in, with 100mm blockwork in between, this was added later and built up to and cut round the joists, so takes very little (if any) of the roof load.

The lean to roof in the pic will have additional joists added between the existing, and will be covered with 2 layers of 18mm OSB and 2 layers felt.
The wall at 'this' end (nearest the camera) will also take the 'edge' of the roof as this is made from trench blocks.

The new joists will need supporting without using the existing wall, so internal posts will be required for each joist, that's about 5-6 in total. They will need a suitably sized baseplate, and should protrude into the room as little as possible.

The roof area is 6m x 3.3m and about 1/10 pitch.
Anyone know what snow loading is likely to be on this?

Was thinking along the lines of 2.3m 76x5mm chs (tube) with a flat welded at the top to bolt the joist into. (one of these per new joist)

On the right track or way off?

Long wall from main doors

• turnitup
• 24 Nov 2010
• 1

 

[hotrod]

Anyone know what snow loading is likely to be on this?

Was thinking along the lines of 2.3m 76x5mm chs (tube) with a flat welded at the top to bolt the joist into. (one of these per new joist)

On the right track or way off?

Thought snow loading design was location specific Deluks. I seem to remember scanning through a doc with a map of the UK on and all these different "zones" for separate areas of the UK. Not sure how it would alter the end design of the solution though, but it may be worth popping the site location down in case a proper SE pops in for a gander.

 

[RonnyRaygun]

...it may be worth popping the site location down in case a proper SE pops in for a gander.

As a proper SE doesn't seem to be around at the moment the apprentice will have to have a go...

In all my (not many) years experience I've never done a snow load calc, and have always taken a load of 0.75kN/m2 for roofs of 30 degree pitch or less.
Anyway, I guess now's as good a time as any to have a first attempt, so I've just done the snow calc based on surrey as a location and an altitude of 250m (not going to be much more than that in Surrey), and the load come out at less than 0.75kN/m2. Up in Scotland or the Lake district the snow load is going to be much more of an issue...

Anyway, a 76x5 CHS will be plenty strong enough to support the loads we're talking about.

 

[jeds]

As ronny says 0.75kN/m² is the standard for altitudes below 100m or 1.0kN/m² for certain areas between 100 and 200m. I'm not 100% sure but I think Surrey could be in the 1.0kN zone?

Either way 5 or 6 75x5mm SHS posts is way over what you need. I bet you could quadruple the load and you'd be still well inside.

 

[big-all]

leith hill highest point in surrey 300m above sea level
http://en.wikipedia.org/wiki/Leith_Hill

next highest is indeed around 250m

 

[RonnyRaygun]

As ronny says 0.75kN/m² is the standard for altitudes below 100m or 1.0kN/m² for certain areas between 100 and 200m. I'm not 100% sure but I think Surrey could be in the 1.0kN zone?

Didn't know that. Is that in BS 6399?

 

[Deluks]

Banstead, approx 125m and sheltered (residential) location.
Useful replies thus far, keep 'em coming!

 

[jeds]

As ronny says 0.75kN/m² is the standard for altitudes below 100m or 1.0kN/m² for certain areas between 100 and 200m. I'm not 100% sure but I think Surrey could be in the 1.0kN zone?

Didn't know that. Is that in BS 6399?

Well, I'm referring to the TRADA span table for small domestic works (in effect, Bregs Part A) but the span table takes them from BS6399.