Nowadays when sales are moving into the web and time is precious as never before a lot of garage doors’ dealers are selling garage doors even without measuring. That means the only thing – the end-user is responsible for exact figures when placing an order. Personnel problem exists as well. It takes time to train a rookie and make him remember all technical nuances of the garage door business. Without having enough practice, the possibility of making a mistake is quite high. The mixture of door types, gears, designs allows to pick up the right door for each customer, but also requires a good technical background as well.

Eventually, a professionally made site survey helps to make the right choice and minimize error chance in whole ordering chain starting with surveyor-sales manager-office assistant-manufacturer-installer up to end-user.

Most important, on this page you can find the main garage door measuring tips with specific details for each of 3 main garage door types: sectional, side-hinged and sliding. And two installation positions: ‘behind reveal’ and ‘in-between’ the opening.

On Picture 1 the red line shows ‘in-between’ and the blue one – ‘behind reveal’ installation positions.

You can fit sectional garage doors behind reveal and in-between. Side-hinged doors usually you can fit in-between but in special cases behind reveal or on the front wall. Finally, sliding garage doors are installed behind reveal only.

Site Survey -Installation Position
1. Garage Door Installation Position

Basic Observations

There are 6 basic measurements and observations to be done during the site survey.
Check Picture 2 (view from the inside of garage):
W          – width of the opening,
H           – the height of the opening,
OH        – the height of the headroom, usually it is the height of lintel,
SL, SR   – free space on left & right side-rooms,
D           – garage depth – free space on the ceiling.
RW        – reveal width,

Also please take measurements in several places and write down accurately. Even more, in unusual or complicated cases take pictures. It will be easier later to find out the technical solution.
These basic measurements are important for all garage door types.

Site Survey - Opening View From Inside
2. Opening View From Inside
Site Survey - Garage Space Side View
3. Garage Space Side View

Picture 3 shows more measurements to be taken. So ignorance of garage door depth or downwards sloping ceiling lead to expensive mistakes.

On Picture 4 you can see why it is important to measure in several places and to check are the walls plumb, floor and lintels level. Please measure in a few places, because you can find different sizes in different places in the opening. Size matters, really!

Black lines depict irregular quadrilateral shape opening. The flaws in the picture are exaggerated but that shape opening could also be made on purpose as well. Actually the same is with arched openings. In fact here you can see how different doors can be. Red rectangular shows the correct door size if installed in between and the green one if door installed behind reveal. For installation behind reveal – consider the biggest measure. For installation in between – consider the shortest. Please don’t forget to deduct at least 10 mm from width and height for tolerance if the overall frame size is used for ordering.

Site Survey - Opening Shapes
4. Opening Shapes

Headroom & Side-rooms

Very important for doors installed behind reveal – sectionals and sliding. Of course, headroom & side-rooms must be on one plane and plumb. Take picture and measure if part of the surface is jutted out or deepened. Usually, it can be sorted out with timber or plaster.

For sectional doors, critical is at least 150 mm of lintel and 100 mm of the side-room. For sliding garage doors – 120 mm of lintel and whole side-room on the door opening side. Just document the existing situation. Check exact technical data for each door type. If some parts are too short or missing we can offer many means how to resolve it.
Usually, the lintel and side-rooms are the favourited places to mount pipes, cables, gas meters or other obstacles. Please measure distance up to the obstacle.  Secondary lintel, ventilation or sewage pipes could cause problems as well.
Pictures 5-8 show some situation examples and how to measure up to the obstacle.

Site Survey - Headroom1
5. Pipe On Lintel
Site Survey - Headroom2
6. Secondary Lintel
Site Survey - Headroom3
7. Ventilation/Sewage Pipe
Site Survey - Headroom4
8. Lintel Not In One plane

In case of sideways sloping roof please take measurements as shown on Picture 9. The yellow lines show measuring guides for the sectional garage door. Vertical yellow is 100+ mm from the reveal edge. The red lines are for the sliding garage door.

Site Survey - Headroom5
9. Side-Sloping Roof

Ceiling, Garage Depth & Space

Both sectional and sliding doors require specific installation depth. It can vary depending on headroom for sectional and side-room for sliding garage doors. In any case, the garage door depth D (Picture 3) must be measured.
Also, check if the ceiling is level. If the ceiling is sloping down (Picture 10), it is necessary to measure the ceiling height at a specific distance from the lintel.

Site Survey - Sloping Down roof
10. Sloping Down Roof

For the sectional door, it is H+1 metre and for the sliding door, it is W + 1 metre. Knowing the ceiling height at a specified distance you can find out if the door will fit.

Please observe garage space where guiding rails or tracks will be installed and the door will be moving during the operation. Check for pillars, support constructions, curved or narrowing walls, non-rectangular shape, racks, shelves, boilers, etc.

Lucky you if the garage space is nice and clean. But if not, please take all possible measurements. Picture 11 shows some possible situations.

Site Survey - Garage Plan
11. Garage Floor Plan

Windows & Doors on Side Walls

A common mistake is to ignore existing windows and doors on the side walls. If there are doors and windows, make drawings with measurements, mark opening directions, take pictures. The customer won’t be happy if after garage door installation the side door will be blocked, or windows shaded. Having the information, you’ll be able to explain to the customer what is necessary to rearrange or what inconveniences could arise. Customer, knowing and accepting all circumstances in advance, will not be able to complain after installation. On the other hand, having all the information you will be able to offer the best possible solution.

Pictures 12-14 illustrate just one example and how measurements should be taken.

Site Survey - Floor-plan
12. Floor Plan - Windows & Side Door
Site Survey - Windows
13. Windows
Site Survey - Side Door
14. Side Door

Reveal width

An important measuring for sectional garage doors installed in-between. Wide reveals can cause additional problems for doors with electric openers and for some track systems. Accordingly, knowing the reveal width, you can choose the best combination of frame lintel height, track type and door opener.

Pitch Roof

Some garages have a pitched roof. We can manufacture sectional garage doors with ‘pitched tracks’ to go along the roofline. It is a perfect space-saving option. In this case, you must find out and specify the slope angle. At first glance, it could seem a bit complicated if you are not familiar with trigonometry.
On Picture 15 shows the angle you have to calculate.
The formula is A = arctg ( H2 / L ).
For example, L can be 1 metre or 2 metres or any other size which is convenient to measure. Just mark the point on the floor and measure the distance from that point to the wall (L) and distance to the ceiling (H1).
H2 = H1 – OH – H.

To calculate the angle use your scientific calculator or Excel formula =DEGREES(ATAN(H2/L)), or simply search the web for ‘trigonometry calculator’ to find out the angle.

Site Survey - Pitch Roof
15. Pitch Roof

Corners & Shape

Most of the garages usually have regular rectangular shape with right–angle corners. But if you see that there is something wrong, check if garage side walls are at the same distance on both ends of the garage. If the garage is narrowing, for the sectional garage door you have to take side-room measurements like on Picture 10. Please check the corners alongside the opening. For sectional garage doors, it is important to avoid horizontal track clashing with the sidewall.

Sliding doors as a standard are made with the right-angle corner but can be made with acute or obtuse corners as well. You have to measure the angle to specify in the order.
Picture 16 shows the parallelogram shape garage with one obtuse B and one acute C angle alongside the opening.

Measurements and calculations are similar as for the pitch roof angle.
B = 90° + arctg ( L2 / L1 )
C = arctg ( L3 / L4 )
Surely, there must be the right angle ( 90° ) between ‘triangle’ sides L1-L2 & L3-L4.

Site Survey - Irregular Shape
16. Irregular Shape

Floor & Driveway Level

Also check if the floor is level. Quite often case on side sloping driveways.
Very light slope acceptable for hinged doors if the garage is not used for cars. Up to 5 mm difference between corners you can compensate with packers during installation. But keep in mind – the frame must be made according to the shortest measure to fit into the opening.

Indeed, you can order sectional garage door with incline cut bottom section replicating slope. Accordingly, you must specify the height difference in the corners. Best of all make a separate drawing to avoid misunderstandings.
Critical specification for sliding doors. The floor must be level in all directions. At least on the door motion trajectory. If the floor is not level, some cutting and cementing job must be done to get the floor level. For better water drainage garage floor can be made with a slight slope. Accordingly, it will be necessary to cut the groove along the sidewall to get the level floor on door trail.

For side hinged garage doors you should check driveway slope in front of the garage door. Please pay attention if slope looks like on Picture 17.
Door leafs can clash driveway and won’t fully open. In this case the solution could be a raised threshold or bi-folding leafs.

Site Survey - Floor & Driveway
17. Floor & Driveway


Of course, if you see something unusual or you never met in your practice, try to document and measure accurately, take pictures, make drawings.
Please consult the manufacturer for the best possible technical solutions.
Also, read manufacturers technical data and specifications to see the necessary space requirements for specific door type.