Ventilation of large garage

[kylegordon]

I'm lucky enough to be getting an insulated steel 8x8.5x5 garage built, floorspace of 68m2 and volume of 261.6m3 (5m peak). I'm just working through the building warrant requests, and am stumbling at ventilation. Whilst it's for cars, it's also to be my workshop, so I'd like to keep the heat in.

They have referenced CIBSE Guide B2: 2001, which I don't have, but they have kindly provided a few paragraphs, roughly stating that it must be 1/20th the floor area of trickle vents, or 6ACH of mechanical ventilation.

The initial suggestion of trickle vents - that would be 3.4m2 of trickle vents. That seems to be... quite a lot! Am I missing something glaringly obvious?

For mechanical ventilation, at 6ACH and if my volume calculations are right, that's 1569.6m3 per hour. I can get a fan and shutter for a few hundred quid that will do the job. Is it the right choice though?

 

[^woody^]

3.4m2 is bigger than my front room window. So that's like me sitting here watching The Chase with a 3.4m2 hole in the wall.

1/20 floor area reference normally relates to area of window/glass in an insulated wall or maybe area of openable window for rapid ventilation, not trickle.

 

[kylegordon]

Yeah, could fit a (small) bus through it!

The building isn't planned to have any windows, but would the doors count in that case? Plenty of ventilation if the pedestrian or main doors are open. I see some references in other documentation to 'purge ventilation' where doors or windows can be opened.

Additionally, I see from https://www.gov.scot/publications/b...-non-domestic/3-environment/3-14-ventilation/ that my volume calculations were wrong too. I can disregard volume above 3m, which reduces the mechanical load a little.

 

[^woody^]

It's Scotland so I'm not familiar with the regs, but they are not too dissimilar to England.

Yes a door counts for rapid/purge ventilation, but surely ventilation standards mentioned are for habitable rooms, not garage/ workshops?

 

[kylegordon]

Well, just to round this one up, the main issue with using doors as ventilation is that 50% of them would have to be on the opposing wall, which this clearly wasn't going to have.

I settled on an extraction fan capable of over 6ACH and operated when occupied, informed that the garage is for the storage of vehicles and household items, and also informed that it would not be a workshop with running engines (10ACH required then), and all was well. It really is just a large residential garage. I have zero desire to be running engines in there!