I was asked this question today, and I can understand where the customer is coming from. I then went on to explain a little bit on the phone, but write here to explain in more detail.
He was thinking door online plus fitting should be circa £700. I would suggest you would be lucky to find one.
The first thing is the quality of the door. Unsure of the standard of what you will get online. There is also the fact that a new door would be a made to measure product, which is likely dearer. There are further direct material costs, silicone, sealant, fixings, trims and potentially add ons.
The direct material cost dealt with, now to the labour. One would have to get a survey of the door before ordering. The surveyor would run a van and have kit. Then you would need to pay the labour for the installation.
Registration with the local authority. This is a requirement under building regulations. There are several self certification schemes, FENSA, CERTASS etc – (Think of GAS Safe to Gas).
Then there is a guarantee. Industry wide the standard is ten years.
There are also indirect costs. Such as storage premises, showrooms, administration (needed to order the door correctly).
Companies also have to have a marketing budget to ensure people know about their services.
A fair price? Difficult to define, but it is reasonable to allow enough for an installation company or individual to allow for all the associated costs and make a profit.
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