I'm planning to replace a window in the gable end wall of my house with an external door. Not sure whether or not I need to employ a structural engineer, or whether the builder will cover this. If it makes any difference, it's a single storey detached welsh 'long' cottage, about 300 years old and built out of rubble stone.

Any advice?

Are yo making the opening any wider or merely extending it downward? If the later it is simpler.

However have you checked for building warrant / planning issues?

I'd say unless you are doing work which requires a new lintel, you will be ok. Otherwise, at the very least get some loading calc's from Catnic or the like.

I think the opening will have to be extended both below and above the height of the existing window, so probably a new lintel.

erm .. sorry to sound completely dense but are 'loading calc's' something that I could do?

If you don't know what they are then I would suggest you shouldn't be doing them

they are calculations of thr load that will be imposed, which will be used to inform the decision on the structural changes needed. I.e. if you get it wrong, your house will collapse. Get a pro in.

Dont fall foul of Cadw, I would check if you need planning or any other such permission for altering the building.

nbt – "If you don't know what they are then I would suggest you shouldn't be doing them" ah, yes, I had that thought when I typed the question 🙂

looking more like I'd need a structural engineer – in which case is there an 'approved body' or qualification that I should be looking for?

Would I also be right in tinking that I will be needing approval from building control? Don't think I'd need planning permission – the house isn't listed, so no concerns from Cadw, and its just outside the edge of the National park boundary so less restrictions

if the door is no wider than the existing window I don't see how there can be structural issues unless the new lintel is made of cardboard…

if the opening is going to be wider than the existing then it would be beneficial to get advice from a structural engineer (if you speak to the local authorities building regs department they should be able to recommend someone local as well as say if you need planning consent, building regs etc.

If the opening is the same width but higher, in theory the existing lintel can be reused as the new loading will be less than the existing.

As mentioned above, speaking to Catnic could explain any issues you might encounter.

Sue – the IStructE is the professional body for stuctural engineers – their website has a 'need an engineer' link on it.

Providing you are using a competent builder expereienced in modifying stone houses, I relly wouldn't bother with structural calcs. From the description of your cottage, presumably with a some what informal construction, the difficult bit will be making the opening without the gable end falling down !

Marcus – yes "informal construction" just about sums it up – it was originally built as a mountain 'hafod' – a summer dwelling in the hills for sheep farmers when they moved the sheep up from the valley in the summer. I think the end that the external door will go in used to be the shelter for the sheep, but is now a kitchen. The walls are built with hand-sized rubble stone (and a few boulders and bits of bedrock that are still in the ground) held together with old mortar which is common to similar old hillside cottages in Snowdonia – so I'm not sure if 'standard' approaches to calculating loads would work?

Sounds shonky I know, but the view is fantastic 🙂

Sounds a great place, a little difficult to keep warm on a cold windy day i should imagine.

I also cant really see how any formal loading calculation could be done by an engineer without being overly conservative. – It is one of those situations where using an experienced builder is more important.

It depends how strict your local council are, they might require to see calculations which can only be submitted by a Charted Structural Engineer.

go could try asking here:
http://www.newbuilder.co.uk
Lots of knowledgeable construction types on the forum.