Struggling Building a Garage Maximum 2.5m High

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Hi all....a newbie on here but I've read loads of threads that have helped or gave valuable information over the years.

We're building a detached flat roof garage under permitted development and as it's within 2m of the boundary, it can't exceed 2.5m in height.

The dimensions are 4.5m wide and 5.2m long with the garage door at one of the 4.5m ends. What we're struggling with is trying to get the roof height dimensions as compact as possible to give us as much headroom and garage door height as we can.

What I mean by that is if we allow 25mm ply and EPDM, 150mm firring (to allow a 1 in 40 fall from front of garage to rear) and 225x47 joists (necessary to cover a 5.2m span), we're calculating a wall height of 2100mm. I'm reading that generally, garage doors require 300mm+ of headroom for the mechanism etc. so we're down to 1.8m high garage door......which seems low to me.

Anyone else dealt with this type of scenario? Any solutions to try and create a taller wall height?

We were thinking of installing a 152 rsj across the width in the middle thereby cutting the length of joists in half so we wouldn't need 225mm joists but could use 145x47 joists thereby shaving 80mm off the height. Might need help to calculate if this is OK? Instead of adding firrings to the flat roof, I suppose we could set the wall at the garage door end higher and have the roof run down to the rear. That would raise the front wall above the garage door by 150mm giving more room for the mechanism. Any advice would be appreciated...
 
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My neighbour has a new garage door - the mechanism is within the 50mm frame @ the top - are you thinking of a roller shutter one ?
 
Possibly......but the 300mm headroom seemed generic advice?

I was looking up electric garage doors and the roller/shutter type came up the most. Some were requiring 450mm and others 300mm. It's not imperative that we have a roller door. The sectional doors look good. But we'll have to have what fits I guess. The reasoning behind a sectional or roller door was that we wouldn't have to think about how close we park in front of the door as we are limited on parking space between the gates and the garage.

Edit.....a quick look on the net and it's being suggested a sectional garage door requires 100-220mm for the curvature of the track.
 
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Why must it slope from front to back?
It could go side to side with less of a heigh difference

Some sectional doors can be used close to the ceiling
A neighbour has a roller door with the gear outside, boxed in
 
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Why must it slope from front to back?
It could go side to side with less of a heigh difference

4.5m vs 5.2m span.... it’s 8x2 vs 9x2 so 25mm. Plus the slope will go across the door so asthetics come into play plus I don’t really gain much above the door itself whereas if I start the slope above the door, I could gain interior height where I need it.

Some sectional doors can be used close to the ceiling
A neighbour has a roller door with the gear outside, boxed in

Not seen roller mechanisms outside. And if 300-450mm is accurate, it’ll sit above the roof line.

I expect the sectional door runners to run across the ceiling but as expressed upthread, there’s the curve of the runners and it seems depending on the door manufacturer, that could be 100-220mm. At least it’s heading in the right direction.
 
Off the net
 

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Have you started building already? If you're that tight for headroom, you could always lower ground levels to get more usable height. Challenge would be keeping it dry.
 
Have you started building already? If you're that tight for headroom, you could always lower ground levels to get more usable height. Challenge would be keeping it dry.

Yeah, we've already started. We poured the slab the other day and the brickie has already laid the first few courses of blocks. I deliberately shuttered the slab to keep it out of the soil in an effort to keep it dry.

The more I think about it, the more I think it's the best idea to build the garage door wall up higher to create the fall of the roof line for water run off instead of using firrings. That way, it creates 150mm of usable ceiling height at the door end. And I'm inclined to place an rsj on pillars in the middle of the garage shortening the span each side which should allow me to run 6x2 joists instead of 9x2's.
 
The more I think about it, the more I think it's the best idea to build the garage door wall up higher to create the fall of the roof line for water run off instead of using firrings. That way, it creates 150mm of usable ceiling height at the door end. And I'm inclined to place an rsj on pillars in the middle of the garage shortening the span each side which should allow me to run 6x2 joists instead of 9x2's.

My last garage was built like this - it was just over 4M wide and the side wall was a single brick higher than the opposite side, with 200mm joists. Incidentally, that arrangement also made it easy to convert to a pitched roof at a later date just by adding rafters.
 
If you're really desperate for every inch you could do away with the 6x2's all together and put some steel box section in instead... It's not that expensive... I've no idea what size they would need to be, but maybe save you two or three inches...
 
What about some good heavy barn doors and a small pedestrian door to the side - so you can get inside on foot with cars parked up against the doors
 
just a thought if you are using a roller door that rolls up to say 300m
then hows about a cross beam 350 back to give clearance with the roof timbers supported off this and only the say 18mm osb or ply between the roller and the felt
so most off the roller will be above the lowest edge off the timbers in a pocket
 
Unless you have difficult neighbours build up a bit of ground round the back and build it a few bricks higher.
 
Have you checked your measurement from the highest adjacent ground?

On planning permission height is taken from the highest point, which you can state.

how about a central steel of 4.5M, then joists of 2.6M -as you said in your OP? -the joists could be set at the fall you need.
 

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