Anyone know about if building regs specify thickness of external glazed doors?

[westtwo]

I am converting a very large open-plan studio flat into a proper one bed. My bedroom is going to use all of the current very large kitchen space and bit of the lounge. The front door which was an entrance into the kitchen will be moved further down the flat's front wall and I will use the existing opening of the front door to create a full-length glazed door with a window above. The door will open out onto a garden at ground floor level. I had planned to use the existing frame for the front door and also this already has a window across the top. I have listed building consent and planning and today a joiner has told me he thinks I can't keep the existing frame because the door width that fits it is 35mm and building regs states external doors have to have 50 mm thickness. I have been googling and can't find anything on door thickness. This is an external door but is not my main front door. My listed building consent did not comment on me retaining the frame, though we did say we will be fitting a new door to match the style of the existing one as the front door was glazed with opaque glass with a frame all the way around and we will use the same style but just have clear toughened glass). I would be grateful if anyone here can point me in the relevant direction of the building regs please as I don't know if he is correct and another guy came to quote and said he thought it would be ok to use the existing frame.

Thank-you in advance if anyone can help!

External doors usually are 44mm thick finished (50.8mm nominal), and will not fit an internal frame. Internal frames are also not designed to resist rain or intruders so it would not be a good idea to attempt to use it.

The building regulation he is thinking of is probably about insulation properties of external doors and windows, afaik there is a performance spec but not a thickness spec. It might be possible at great expense to find a thin door that meets it. It would be difficult but not impossible to find a burglar-resisting lock that could be fixed to a thin door.

A new frame will not be a significant cost in your scheme. Why don't you want one?

Thanks so much for reply piglet john. The frame I wished to keep is for an external door, it's for my old front door and I am fitting a new full length door but this door will be a door to a bedroom rather than a main entrance. I wanted to reuse the existing frame as it already has a window above. It seems a bit of a waste to remove that frame and replace it with one that is identical in every respect except the thickness of door. I have been told I have to have double glazing and toughened (safety) glass so by the time I have all that will that mean I will have to have a thicker door than 35mm?
Thanks again?

I don't think I have ever seen an thin internal door with DG. Perhaps you could if it was metal. The unit will be about 6mm glass

• 18mm +6mm glass = 30mm thick so how will it fit in a thin door? Even if it was just 25mm thick there is hardly any room for a rebate.

A photo of the frame showing profile and dimensions might help.

BTW ask about having a laminated glass unit made, it will be more burglar resistant

Thanks so much for the advice. Think there is a bit of confusion I think the door isn't an internal door, when I say a door to the bedroom I meant like a French door that is on an external wall. But yes I will be going for a new frame. A general builder told me I could retain the existing door frame but he was wrong it seems.