Difference between internal and external doors?

[WineWithAView]

The porch on my house is a new-ish addition. So, the inner porch door was the original external door. This needs replacing. I was going to replace it with a part-glazed, wood external door, so that it lets in light but I can still lock it.

Seems though that it would be cheaper to buy an internal door rather than an external door. So, is there any great difference between an internal and external door? And if I buy an internal door, would I still be able to add a decent lock onto it?

Usually solid internal doors have a particleboard core whereas an external door will have an engineered hardwood core. If it isn't exposed to the elements then an internal door would be fine but you need to look carefully at the existing frame. External door frames usually have a built in stop so you would need to replace with the same size and thickness door, or find a way to make it wider. An external door is usually 44mm thick and to get this thickness you will need to get a fire door. A fire door would probably be a good idea anyway in order to accommodate a better insurance rated mortice lock which would have a thicker case but be aware that glazed fire doors are very limited in style and sizes and are usually upwards of £400 so an external door may work out cheaper and easier.

Ah excellent information, thanks so much @Undergroundovergroundwomblingfree. Just what I needed to know.

It might be you still need an external door to satisfy building regulations.