length of flat roof joists

[b21playa]

Hi all

Just starting off the process of planning a rear extension.

At the max depth it will be 5m, and will have a flat roof with some sort of roof windows (as pictured below) which weighs about 55kg each for a 800mm x 800mm

Will any wood joists span that distance safely and cater for a roof window, or will I need an i-beam to split the distance?

 

[loply]

If I'm not mistaken 220x75's if set at 400mm spacings will give you a 5.8m maximum span. Local BCO can probably confirm for you though?

 

[b21playa]

If I'm not mistaken 220x75's if set at 400mm spacings will give you a 5.8m maximum span. Local BCO can probably confirm for you though?

Cheers

As the window is wider then 400mm, would the joists either side be doubled up, just as with velux windows?

 

[skhudy]

There is a joist span table to look at as a guide here
http://www.jrpcad.co.uk/Pages/Timber_Span_Tables.aspx
Are you not using a architect? the structural engineer calculations will tell you

 

[b21playa]

There is a joist span table to look at as a guide here
http://www.jrpcad.co.uk/Pages/Timber_Span_Tables.aspx
Are you not using a architect? the structural engineer calculations will tell you

Yes, using an architect, but only just sorted it out and he's away for a few days.

I just wanted to know, this work isn't starting for a while, Im just curious

 

[Static]

As a guide 75x220 @ 400c/c is probably about right.. but you may well end up with triple trimmers each side.. 5m is a long span even for a roof you dont want it too spongy

 

[b21playa]

As a guide 75x220 @ 400c/c is probably about right.. but you may well end up with triple trimmers each side.. 5m is a long span even for a roof you dont want it too spongy

I guess adding a steel to shorten the lengths would stop the'bounce', but would mean I need a pillar along each wall in order to get a 150mm bearing

 

[Static]

You may not need 150 bearing.. 100 is about minimum without some careful building works..

Look into TJI or JJI joists.. chances are they will be cheaper and they are alot better at the long spans..

 

[b21playa]

You may not need 150 bearing.. 100 is about minimum without some careful building works..

Look into TJI or JJI joists.. chances are they will be cheaper and they are alot better at the long spans..

If 100mm is possible, then thats ok. I could stick with 9x2s but now will be max 3m in length

Like these

http://www.ebay.co.uk/itm/ENGINEERE...ies_Carpentry_Woodwork_ET&hash=item1c2c4bd191

 

[Static]

Yep like those.. but you would need to get it designed.. there are different grades for each depth that can take different loads.. the basic 220 deep joist probably isnt suitable for 5m..

I think they work out similar price to the 9x2 joists but they weigh considerably less.. just adding options..

 

[b21playa]

Yep like those.. but you would need to get it designed.. there are different grades for each depth that can take different loads.. the basic 220 deep joist probably isnt suitable for 5m..

I think they work out similar price to the 9x2 joists but they weigh considerably less.. just adding options..

Thanks

House being measured up in 8th feb. Hoping by end if feb to have some draft plans

 

[catlad]

I like the look of that skylight what make is it.

 

[b21playa]

I like the look of that skylight what make is it.

Not sure mate.

My uncle got one fitted recently to his single storey extension. 2x1m and brings in a lot of light. He got his from a local place where he got his bifold doors from

 

[catlad]

I thought it looked bespoke and a lot bigger than 800x800

 

[b21playa]

I like the look of that skylight what make is it.

http://m.ebay.co.uk/itm/131098973311?nav=SEARCH&sbk=1