How to fit an external door frame

External door frames  are often sold ready-assembled by the manufacturer, and they can be installed using the same basic method you'd use to install a pre-hung door. Remember when an external door frame is being replaced it will be considered a 'controlled fitting' under current Building Regulations. This means you'll have to notify Building Control of your plans or you can use a 'competent person who will be familiar with Regulations. 

If the frame needs assembling on site it's usually called a knockdown frame, or frame kit, and often has the joints pre-cut for convenience. It should be assembled by a competent joiner as you must comply with Building Regulations for external doors when replacing the frame, and not just the door slab. You can use a registered installer who can issue a proof of compliance certificate on completion, or you'll need to pay a fee to the relevant Building Control Body so they can inspect the finished work.

If you do have a frame kit for an external door you should refer to the manufacturer's instructions for your specific frame for details of its installation as not all frames are the same. You will also need to ensure you have taken accurate measurements and have a frame which will fit properly in the rough opening with a minimal gap between the frame and the walls. 

For more information about measuring for the size of a door frame see: How to measure for a new doorset

External frames  can be made of wood, metal, uPVC or fibreglass. The frame pieces might need to be trimmed to size on site. If this is the case you need to make sure you have the correct type of saw to cut the material the frame is made of. You also need to ensure the fixings you use as suitable for the frame and the wall you're fixing it to. All XL Joinery door frames are of an engineered construction, for durability, but have high-quality natural wood veneers for an elegant finish. Choose between oak door frames  and hardwood door frames  to complement the material your door is made of.

Door frame kits  

External door frame kits consist of two side pieces, known as jambs, and a head piece that goes across the top, and a sill which spans the bottom. External frames also usually have the door stops rebated into the jambs, unlike internal frames which usually have separate stop pieces. They should also have weather strips already fitted, or a recess for weather strips to be installed later. Manufacturer's instructions will guide you on weather strip installation.

You should check the rough opening once the old frame is removed – it should be square, or you may need to make adjustments to the opening itself. Openings which are not square can cause the door to fail. You can check the opening is square by measuring diagonally across each corner, these measurements should be within 5mm of each other. You only have a minimal amount of adjustment for fitting external doors.

External door frames need to have a waterproof course or builders membrane installed in the rough opening before any frames or doors are installed.

Step 1 - Assemble frame parts

Lay the frame on a clean, dry floor or appropriate workbench, where there is enough space to assemble it. Fit both jambs into the recesses in the head and sill, and attach weather bar if it's separate. You should use a waterproof adhesive sealant on all joints as well as screwing them together. Check the instructions for anywhere else where sealant also needs to be added.

Check that all parts of the frame are straight, level, and plumb as you fit them. You might need to fit the sill to the rough opening and then fit the rest of the assembled frame, or the sill will be fitted to the frame as you assemble the other parts. Screw the pieces together for a permanent fix, checking the frame remains square as you fix each piece. 

Step 2 - Level floor and caulk opening

Use packers and shims to get a completely level surface to install the frame onto. Squeeze a bead of waterproof caulk around the rough opening, either side and across the top. Use two or three beads at the bottom for the sill. This will help hold the door and will also provide a waterproof seal around it.

Step 3 - Install frame

Carefully lift the frame into the opening. Place the sill in position, with the frame tilted outwards, and push into the opening.   

Step 4 - Level frame

Starting at the bottom of the frame, make sure the sill is completely straight and level, adding any shims as necessary. Check all parts of the frame are aligned correctly, or your door won't operate properly. When the new door slab is fitted there should be a uniform 2mm gap between the top and either side of the frame.

Step 5 - Fix in place

Once the frame is correctly positioned you can use appropriate fixings to secure it in the opening, usually fixing it in four or five places down each jamb and in two or three places in the head. continually checking the frame remains square. The placing of the fixings depends on the type of wall.

To prevent bricks or blocks around the rough opening splitting, the fastenings must be staggered. They should each be fitted about a third of the way in from the edge of the jamb. The instructions should direct you with the correct spacing for your frame. 

Step 6 - Finish

Fill the gap around the frame with insulation, like expanding foam, and seal all round the edges with caulk. The finished frame should have no visible gaps where it joins the wall.