How to Fit Architrave When the Door Is Not Perfectly Square

Most often, internal doors are perfectly square, and this means you only need to cut standard 45-degree mitre joints into the architrave to properly install it.

Sometimes, however, the door frame may not be perfectly square, which means in order to properly fit the architrave you will need to take additional steps to ensure that you cut the pieces of architrave to the correct angle, as a 45-degree mitre, in this case, will not produce the desired outcome.

We've created a video guide to show you how to do this below or if you prefer our step by step guide can also found below.

The process begins in a similar way to the usual process for fitting architrave. You will need to make regular markings around the outside perimeter of the door frame 5mm from the inside edge using a pencil and set square. This ensures the architrave isn’t positioned too close to the opening where it may be damaged by traffic or wear and tear from constantly opening and closing the internal door.

Once you have these markings in place the next stage is to establish how the architrave will need to be positioned when fitted. To do this, hold a piece of architrave upright on the door frame so that the inside edge of the architrave aligns with the 5mm markings, and the length of architrave protrudes beyond the height of the door frame by 20-30cm. With the architrave in position, make a pencil line along the OUTSIDE edge of the architrave. Repeat this process for the second upright.

You will now need to mark the outside edge of the architrave for the ‘header’, so place the piece of architrave you have used to mark the uprights in position along the top of the door frame along your pencil marking, making sure the architrave extends beyond the outside upright pencil marking you just drew. Again, take a pencil and create a line along the uppermost edge of the horizontal architrave, so that it intersects the outside upright pencil line you drew earlier. Again, repeat this process for the other side of the door.

You will now have a complete frame drawn out around the top of the door. Using a straight edge (such as a spirit level) and pencil, draw a diagonal line from the inside corner marking to the outside corner marking at each side of the top of the architrave.

You will now need to transfer the cutting angle from the markings on the wall to the piece of architrave. Begin by using a sliding bevel, and butt this up to the inside of the door frame and adjust the blade so that it follows the diagonal line you marked between the internal and external pencil line intersects. Tighten the bevel so that the angle is locked in. Next, take the length of architrave you are using for the upright and hold it in position so that it runs through the angle you just measured with the bevel. Mark the architrave at the point where it aligns with the marking at the top of the door frame. This will ensure the architrave length is cut to the correct length.

Place the sliding bevel on the inside edge of the architrave length (profile side) and position it so that the blade aligns with the pencil marking on the architrave. Now, using a pencil, draw a line along the blade of the sliding bevel and this will perfectly replicate the diagonal line you drew on the wall. This means that you can confidently cut along this line and know that it will sit on the wall exactly as intended. Repeat this process for the second upright.

For the architrave header, begin by butting the sliding bevel up to the underside of the door frame and adjusting the blade so that it runs through the diagonal line on the wall as before. This will give you the opposite angle to the one on the upright so that when cut both pieces will join seamlessly. Lock the bevel into position as before so the angle can’t move.

As you did with the uprights, hold a piece of architrave along the horizontal markings along the top of the door frame and mark the architrave at both ends where the cuts will be made to bring it to size.

Use the sliding bevel to once again transfer the cutting angle from the wall to the piece of architrave. You will need to do this for both sides of the header length of architrave but be sure not to assume that both ends need to be cut to the same angle! Once you have transferred the first angle to the header use the sliding bevel to measure the angle for the opposite side of the header and repeat the process of transferring the angle to the architrave and mark it in pencil.

You should now have 2 upright lengths of architrave with a diagonal cutting guide marked at one end of each in pencil, and a header length of architrave marked at each end with a cutting angle in pencil. Take the lengths over to the mitre saw and cut along each angle so that each piece is cut to size. Once cut, take them back to the door frame and hold each piece in position to check that the angles align properly, and you are happy with the outcome before fixing into place.

With all 3 sections cut to size and to the correct angle, it is now simply a case of fixing them in position using a grab adhesive or a nail gun or a combination of both. A more detailed description of how to fit architrave can be found here.

About the Author

Kieron Miller is the Managing Director of Skirting 4 U and has been working in the skirting board and online retail industry since 2012. Kieron has been using his extensive product knowledge and problem-solving experience to help both trade and private consumers all over the country find the perfect skirting board products for their projects. He continues to innovate new solutions and product ideas as the market continues to grow.