lenient building control shock

[mcmook]

i'm in the process of renovating a cafe/gallery. the building is 1

1/2 storeys and the upstairs is vacant at present but ultimately we hope to open it up (coombed ceilings). however we are installing heating downstairs and so i want to insulate the roof. i was planning using rigid insulation above and beneath the rafters so i got in touch with my local BC re ventilation. i was surprised to find out because this is a commercial building the ventilation rules do not apply and I am not obliged to install any. however I tend to think that these guidelines are put in place for a reason and of course condensation would be an issue so I DO WANT to ventilate but am just wondering what a sensible solution would be. the rafters are at ~400mm (although they do vary) centres and venting every bay seems excessive. There is no soffit, I would get a vented ridge placed on the top so ventilation would be required at the bottom of the roof.

there are probably 60 bays so i was thinking perhaps venting every third and providing ventilation to the ones either side by drilling holes through the rafters - would this work?

or because there is no soffit maybe removing stones (stone wall exterior) from the top of of the wall.

any recommendations greatly appreciated?

[Dave Fawthrop]

|!i'm in the process of renovating a cafe/gallery. the building is 1 |!1/2 storeys and the upstairs is vacant at present but ultimately we |!hope to open it up (coombed ceilings). however we are installing |!heating downstairs and so i want to insulate the roof. i was planning |!using rigid insulation above and beneath the rafters so i got in touch |!with my local BC re ventilation. i was surprised to find out because |!this is a commercial building the ventilation rules do not apply and I |!am not obliged to install any. however I tend to think that these |!guidelines are put in place for a reason and of course condensation |!would be an issue so I DO WANT to ventilate but am just wondering what |!a sensible solution would be. the rafters are at ~400mm (although |!they do vary) centres and venting every bay seems excessive. There is |!no soffit, I would get a vented ridge placed on the top so ventilation |!would be required at the bottom of the roof. |! |!there are probably 60 bays so i was thinking perhaps venting every |!third and providing ventilation to the ones either side by drilling |!holes through the rafters - would this work? |! |!or because there is no soffit maybe removing stones (stone wall |!exterior) from the top of of the wall. |! |!any recommendations greatly appreciated?

You will be covered by the Health and Safety at Work Act. Why not contact the Health and Safety Executive?

you are intending to use the premises as a cafe, you will have to satisfy the local Environmental Health Officers eventually, why not contact them first and gain a few brownie points.

[mcmook]

towww.hyphenologist.co.uk/songs/http://www.gutenberg.org/author/John_Hartleyhttp://www.gutenberg.org/author/F_W_Moormani have already been in touch with environmental health - they are satisfied with how we are proposing to refit the kitchen - upstairs will be a gallery i just want to make sure i put in place measures to minimise condensation risks while maximising insulation.

[Alex]

building regs require a 50mm ventilated space above any insulation added to rafters,and this needs to be fixed so that the space can not be compromised,this is done by adding battens,to prevent the insulation moving

are you saying that rafters are open at soffit,if so I would add a facia and soffit then ventilate this space difficult without pictures.

all the above is for residential,

[John Rumm]

First question is does the roof have any sarking under the tiles? If not then job done!

[mcmook]

yes there is sarking, its actually 3 roofs because historically its been added to over the years (long time ago) the first section and mid section has what seems to be tongue and groove sarking, probably with tar based felt on top of that. the end section newset has sarking through which i can poke a key and touch the slate so this part may not need ventilating. its the first two sections i'm concerned about ventilating - just wondering if there is a way without venting every bay - leaving a 50 mm airgap but then venting between the bays by drilling holes through the rafters?

[Hugo Nebula]

On 16 Feb 2007 03:25:25 -0800, a particular chimpanzee, [e-mail] randomly hit the keyboard and produced:

I must say I'm mystified by this statement. Requirement C2 (and before it F2) has applied to all buildings since 1990, as the primary concern is not the health of the occupants, but the damage to the structure and performance of the building.

It could be that you are merely installing additional insulation to an existing vaulted ceiling. You would not be carrying out a material alteration (ie, making the ventilation any worse than it was before), therefore you are not _required_ to install any additional ventilation. Although, as you will be 'renovating' the roof over more than 25% of its area (by replacing the plaster), you are required to insulate the roof to a minimum standard.

A few solutions present themselves:

1. As pointed out elsewhere, if you don't have roofing felt, it most likely that there will be sufficient ventilation to begin with. If you do have felt, then you can wedge the laps open slightly.
2. If you don't have an overhanging soffit, but you have a fascia, you may be able to lift up the bottom row of tiles and insert a continuous over-fascia vent strip.
3. If the wall is built up to the underside of the tiles, you could remove the top mortar bed and insert some vents in there.