How to Fit an External Door

Every exterior door is an important part of your home. It is one of the few exterior design flourishes you can add - it also prevents heat loss and keeps the wind, rain and cold air out of your home. It also protects your home, stopping strangers from letting themselves into your space.

All these factors mean you need to make sure your external doors are always in excellent shape. This means regularly maintaining and repairing them but it also means replacing them promptly when they start to lose their shine and efficiency.

When it comes to replacing exterior doors, most people focus on the process of buying a new external door. But knowing how to fit them is just as important. Knowing how much it can cost to install can affect your budget for the new door itself, and if you decide to install it alone then the difficulty of certain door types could also impact your choice.

We've put together this guide to help you understand all the factors involved in fitting an external door, from costs, to process to difficulty level. Read on to help you make an informed decision when you're looking to buy a new external door.

Is it easy to fit an external door?

Fitting an external door can be a difficult task and, unlike fitting internal doors, it is important you get it right. As external doors and frames are key players in the security and insulation your home provides, they need to have a flush, safe fit. They are also subject to building regulations.

How much does it cost to install a new external door?

Fitting an external door can take anything between 4-6 hours, so you should expect to pay a professional a full day rate to get the job done. According to Ideal Home this can range anywhere from £150-£1500.

The weight of external doors, the complexity of multi-point mortice locks and the need to meet building regulations are all reflected in the time it takes to fit an external door. And the time will affect the cost.. If you buy a pre-hung door with an already assembled frame, you may find it is a quicker - and thus cheaper - job.

Can I install a front door myself?

It is possible to install a front door yourself rather than getting a professional, but it is not advised. All external doors are covered by legal building regulations which state they must provide a moisture-proof seal between the wall, the door frame and the door - this can be difficult to achieve without the right tools and experience.

When you want to install your exterior doors yourself, it can be beneficial to get a prehung door. A prehung door comes already fitted in the frame and it is a lot easier to fit a frame place than it is to hang a door slab into a frame.

With a pre-hung door, all you need to do to meet building regulations is make sure that it is adequately sealed. This can easily be done using expanding foam insulation and silicone caulking to create a weatherproof barrier.

If you do need to add a new door slab to an existing frame it is advisable to get assistance from a professional.

How do you install an external door?

Here is a step-by-step guide on how to fit an external door.

Check the condition of the rough opening

Whether you are installing a new door for the first time or replacing an existing exterior door, you should check the door opening closely before trying to install a new external door frame. It is a waste of time fitting an external door if the opening is damaged as the lifespan and functioning of the new door will be affected.

Install the door frame

If you need to fit a new door frame, this is obviously the first thing you should do. There are a few major differences between fitting an internal door frame and an external door frame, see below for tips.

Measure your new door and adjust if necessary

If you are removing an existing door you can use this as a template to check the size and mark up your new door. If you are replacing both the door and the frame, you should mark up before you start just to be on the safe side.

For minor door adjustments, just trim down the hanging edge and/or the top of the new door. It will be less noticeable there. If you need to make more substantial alterations, take half off each side.

Regardless of which part of the door you trim, make sure you refinish the affected edges. You need your door to stay sealed against moisture otherwise it will swell, rot and no longer fit flush or be secure. Add a couple of coats to make sure you have a complete seal.

Prepare the hinges

Once you have trimmed the door, you can mark out then notch the spaces for your hinge plates. Use a sharp chisel to carefully cut out a space for the hinges to sit while staying flat for the door. If you have a new door frame, you should do the external door frame at the same time. If you are reusing an old frame make sure your new hinges match up.

Attach the hinges

When it comes to external doors you should always use three sets of hinges, particularly for heavy composite or wooden doors. This gives your door three points of contact to distribute the weight and will protect the look and functioning of the door. Washered hinges are the correct type to use for heavy exterior doors and you should make sure to use long, heavyweight screws too.

Hang the door

Move the door into position and start to fix it in place. Put one screw into each hinge at first, check the door is square, opens and closes properly then add the remaining screws.

Fit the rest of your door furniture and hardware

At this point, it's easier to add your door handles, locks and latch plates. Make sure to use accurate measurements to place them, and make sure they are fitted to a stile that is wide enough.

How do you frame an external door?

Many people choose to buy their external doors already hung, in which case you need to install the door frame into your rough opening with the door frame already attached. In fact, even if you choose not to buy a pre-hung door, you can still buy a pre-assembled door frame which is a lot quicker and easier to fit and gives a stronger, more secure finish.

How do you install an external door frame?

Check the condition of the rough opening.
As well as the door sill. Make any necessary repairs or replacements.

Lift the frame into the rough opening.
Take care if using a pre-hung door as it will be heavy. Once in place, check the sides and top are level. If they aren't, use shims between the opening and the outside of the frame to make it level

Screw the frame in place.
If using a prehung door, start by screwing in under the hinges first, one screw at a time. Move on to the lock side and do the top last. After each screw is in place, check the squareness of the door again, and level out again if necessary. Then fix all the remaining screws in place.

If you are installing a separate door slab, fit that using the steps above.

Fill any gaps around the door frame using expanding foam.

Do it with the door closed and be slow, careful and controlled with the foam - if you use too much it can cause the frame to pop or snap.

When the foam has dried, use silicone caulk to beaten the edges and create a fully waterproof seal over the foam.

How to fit an external door frame kit?

If you can't get a preassembled door frame, a frame kit makes another easy-to-fit alternative. These are readily available and make a good secure, safe option and often come already fitted with weather strips.

With an external door frame kit, it is best to put it together before installing it. Make sure it is square and stable before putting it together the same way you would a shop-bought assembled frame.

How much gap is needed between door and frame?

As with internal doors, you need to leave a 2-3mm gap around the sides between the slab and the frame when fitting external doors. However, unlike interior doors, you need to be more careful with the bottom of your door. A large gap between the sill and the bottom of your door will let warm air escape, cold air sneak in and seriously compromise the energy efficiency of your door.

A weather bar is one way to tackle this issue. These external accessories are strips that fit against the bottom of your door to stop water and cold air from getting through any gap between the sill and the door.