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This will vary quite a bit but there are some general sizes for most roller doors to work with.
As there are basically 2 types of roller garage doors available for domestic use in the UK and one is manufactured from single skin sheet steel and the other from individual double skinned aluminium foam filled slats there are 2 different headroom requirements in general.
For the basic single skin steel roller doors manufactured almost exclusively by Gliderol the headroom requirement for a 'normal' height door is going to be around 430mm, and more as the door gets higher. The height is determined as the height to the stop in the side guides and not the total height with the curtain roll.
For the aluminium double skinned type roller door using a 75mm slat with a depth of 19mm (general size used) the headroom required is 300mm minimum in order to get almost the full height as ordered. With ANY roller door there is a section of the bottom of the curtain always hanging down into the opening to get full clearance you need to order the door height about 50mm more than you need and then allow 350mm inside the garage for the roll.
There are 'compact' versions of the aluminium roller doors where the headroom requirement is less at about 210mm with the same 50mm hang down issue to remember. Be careful and do not get focussed on the slimmer slat just because of your headroom available as they are definitely never going to be as good as the bigger stronger slat of the standard doors but they can be a good option when headroom is critical. If maximum opening height is needed and headroom is a major issue then look at the SWS Seceuroglide Compact or the Gliderol compact models.
Of course when you do not have sufficient headroom for any of the roller doors it does not mean you cannot install one. You simply have to be aware you may need some kind of fascia to cloak the gap that may be present, in other words create your own extended headroom section. All the aluminium roller doors sold will have an option for a half or full box cover of you are short on headroom and this gives you a fascia section automatically as well as enclosing the roll with better weather sealing properties. The Hormann Rollmatic and the Garador GaraRoll have full hood covers as standard.
Call us if in doubt as there are a lot of roller garage doors promoted throughout the UK.