Rooflights - Minimum Clear Width

bemak

Very quick question. I'm in the process of designing an attic conversion for a friend and I was doing a bit of research on the minimum clear width required for a rooflight so that it can be classified as a valid means of escape. Part B suggests that it must have a minimum clear width and height of 450mm with a minimum area of 0.33sqm and be between 600-1100 off the floor.

However, in a guidance document about loft conversions (which a lot of the County Councils are providing on their sites) the minimum clear width of rooflights is given as 500 x 850mm. Link to doc here: http://kildare.ie/CountyCouncil/Planning/PlanningLeaflets/LinkToDocument,12869,en.pdf

I can't seem to find this update in Part B so I was just wondering where this new figure of 500x850 has come from.

Thanks!

Gumbo

bemak wrote: »

Very quick question. I'm in the process of designing an attic conversion for a friend and I was doing a bit of research on the minimum clear width required for a rooflight so that it can be classified as a valid means of escape. Part B suggests that it must have a minimum clear width and height of 450mm with a minimum area of 0.33sqm and be between 600-1100 off the floor.

However, in a guidance document about loft conversions (which a lot of the County Councils are providing on their sites) the minimum clear width of rooflights is given as 500 x 850mm. Link to doc here: http://kildare.ie/CountyCouncil/Planning/PlanningLeaflets/LinkToDocument,12869,en.pdf

I can't seem to find this update in Part B so I was just wondering where this new figure of 500x850 has come from.

Thanks!

Rooflights have to be treated slightly different because of their sloped nature. the angle of the window in the roof plane brought our horizontally is the real effective clear width and this is what its aiming for. Its also a rescue window so a fireman may be coming at you from the outside.

Don't forget it must be top hung too, and only one window up there needs to meet this requirement. You can have smaller ones in addition to the one escape window, that should offset the cost some what.

bemak

kceire wrote: »

Rooflights have to be treated slightly different because of their sloped nature. the angle of the window in the roof plane brought our horizontally is the real effective clear width and this is what its aiming for. Its also a rescue window so a fireman may be coming at you from the outside.

Don't forget it must be top hung too, and only one window up there needs to meet this requirement. You can have smaller ones in addition to the one escape window, that should offset the cost some what.

Thanks for getting back to me! I took further measurements yesterday and all the existing skylights are 1400 off the floor - and they're all centre pivot. When you say you only need one window to meet the requirement I presume you mean one window per room!? That's what I'd be aiming for anyway.

Gumbo

bemak wrote: »

Thanks for getting back to me! I took further measurements yesterday and all the existing skylights are 1400 off the floor - and they're all centre pivot. When you say you only need one window to meet the requirement I presume you mean one window per room!? That's what I'd be aiming for anyway.

Yes, at least one window per room needs to meet the regs. At 1400mm and centre pivot, they do not comply. They also need to be max of 1700mm from the eaves externally.

bemak

Is it a big job to cut a purlin in order to achieve the 600-1100 'sill' height?

Gumbo

bemak wrote: »

Is it a big job to cut a purlin in order to achieve the 600-1100 'sill' height?

Your Engineer will advise on that.
If you cut the purlin, the loads have to be transferred and spread evenly somewhere else. Get advice from an Engineer who has called out to view the current roof profile. It may be a simple support issue depending on the floor there.

what size are the floor joists in the attic?

bemak

floor joists are 220mm - so substantial enough. I've advised that the client seek a structural engineer to confirm that the joists are appropriate for the new loads being applied to them - will get confirmation of this purlin issue as well. see pic below of existing scenario.

bemak

FYI - found my answer to the original question.

The PDF pre-dates the revision of Technical Guidance Document B. The 1997 version specified the 850mm x 500mm dimensions. The 2006 revision revised this requirement to "an unobstructed clear open area of 33 sqm with a minimum width and height of 450mm"

bemak

FYI - found my answer to the original question.

The PDF pre-dates the revision of Technical Guidance Document B. The 1997 version specified the 850mm x 500mm dimensions. The 2006 revision revised this requirement to "an unobstructed clear open area of 33 sqm with a minimum width and height of 450mm"

bemak

FYI - found my answer to the original question.

The PDF pre-dates the revision of Technical Guidance Document B. The 1997 version specified the 850mm x 500mm dimensions. The 2006 revision revised this requirement to "an unobstructed clear open area of 0.33 sqm with a minimum width and height of 450mm"