How Much Does it Cost to Knock Through a Door/Doorway or Wall (including video guide at the bottom of the page)

You want to open up the living and dining rooms with a simple “square” opening about 6’ wide. The wall is load bearing but the builder knows the beam he will use (probably a 7”x 4” RSJ or channel), the building inspector agrees with him so there’s no need for a structural engineer to be involved.

Job 1
Now then….hands up if you know what RSJ stands for? Yes Norman…that’s right, it’s “rolled steel joist” isn’t it. Give yourself a house point! Right, time for your homework. What does JCB stand for?

There are no radiators or electrics to move and amazingly, the 2 floors are at exactly the same level as each other, you are clearing both rooms and have even taken up the carpets and are going to put everything back and do all the decorating. (It’ll be finished for next Christmas then)!

This will take 2 men 3 days. Materials will include the steel £75 and the mini skip £75.

Materials £225, labour £750, Building Inspector £125,

Job 2
Same job but this time you want the whole 14’wall out with no nibs and it’s possible (it isn’t always structurally possible, irrespective of the neighbour). One wall is a party wall but your neighbour is friendly but still wants a “Party wall agreement” drawing up which you have to pay for.

This will take the same amount of time plus a bigger steel and the fee to the “party wall” surveyor.

Materials £300, labour £750, Building Inspector £125, Party Wall surveyor £250,

Job 3
Same as job 1 but you want a pair of “off the shelf” multi glazed softwood doors fitted as well. (with lots of safety glass)

Doors, frame, glass, furniture £425, Labour £300, so an extra

Job 4
To reposition a radiator add

Job 5
To reposition two wall sockets and light switches add

A Price Guide and Information Sheet on Knocking Through a Wall and Doorway

Demolishing the interior of our homes is a favourite pastime for many bored householders. It opens up a previously undreamed of vista and makes for that “party home” we’ve always wanted. If only we had the friends to fill it!

However, more than any other building job this must be overseen by the
local authority building regulations engineers office or a similarly qualified person. Knock through without the building inspector - houses, are kept together by the internal walls, knock them down without consultation at your peril!

So you want a through room, what’s the process? First get an experienced builder in and get him to quote for it.

If the relevant wall is timber framed then it’s likely it isn’t load bearing and any amount can be removed without troubling the powers that be.

If it’s a solid (brick or block) wall it
may be load bearing. First of all he should be able to confirm this with a bit of simple measuring and if he’s experienced in these matters he will tell you whether or not you will need to engage an (expensive) independent structural engineer.

Small hole knocks through

If the “hole” you require is only for a set of double doors about 1200mm (4 feet) wide to be put in, then the likelihood is that an experienced bloke will know exactly what size steel lintol to fit and what to rest it on, so no independent structural engineer is necessary.

He will still have to involve the
local authority engineer though, to check his work and once again, if he has local knowledge, he will know if the system will allow him to assess the steel himself (as it’s a small length) for confirmation by the local authority engineer on site, when the job is eventually begun.

If the local authority won’t allow this then an independent structural engineer will have to be involved anyway to calculate the size of steel. (Which will probably be the same as the builder thought in the first place)…… it’s a
game isn’t it!

So, he will now send a quotation and if he has any sense he will assume the worst case scenario for the steel and quote accordingly. That way, if the engineer wants a big old lump fitted, the builder won’t have to come back to you for more cash, which will annoy you and makes him look inexperienced.

Why doesn’t the builder simply phone the local authority engineer first? Because the engineer won’t discuss a job until the authority has been paid to oversee it. At this point the builder has only sent you a quote, he hasn’t even got the job, hasn’t sent in a “building notice” informing the engineers that the job is about to begin and hasn’t paid them.

Entire Wall Removal

If the whole wall is going, then the local authority building regulations engineer will require to see lots of calculations stating why the particular steel beam has been specified. Only a structural engineer can do these calcs. Your builder will wish he could do it, then he would be on £80k a year as well! You should get this done before you get builders quotations, as they will need to know how much to charge you for the beam.

If you want the whole wall to go its very likely you will be disappointed. The steel will have to rest on something at each end, this is usually at least 150mm (6 inches) of brickwork. This will mean some of the original wall has to be left there (called a nib) particularly if one end is a “party wall” These are very often just 100mm thick and also your neighbour will (quite rightly) make a fuss and you will have to get a “party wall agreement” which will probably require
another surveyor.

Single Doorway

If it’s a normal single internal doorway being knocked into an existing wall, you don’t need to involve the local authority, a decent concrete lintol will do but make sure the builder knows what he’s doing. Don’t get the Lone Ranger in!

Questions to ask the builder during his quotation visit.

Will there be a “downstand”?
That’s the bit of the old wall which is left above the new opening, be it just an opening or a complete wall removal. If the wall to be removed is load bearing, it’s much simpler to leave a downstand and it is expensive to remove it. This requires fitting steel between floor joists, supporting through bedroom walls and amalgamating two ceilings. BUT it can be done.

What about the floor levels?
When the wall is gone, two floors that were never designed to touch each other have to be amalgamated. Unfortunately, they will not be level with each other. Even if there is only 5 mm (¼") difference, it will show. There may be two different carpet colours with horrible edges to them.

Whatever is going to be laid all the way through the new enlarged room, (carpet, laminate flooring etc), try and level the floors first, this can be achieved with thin layers of hardboard etc. laid on top of the lowest one.

What about the wall difference?
If you want the whole wall out and don’t need a nib then, just like the 2 floors, two walls that were never designed to touch each other have to be amalgamated. This is done by replastering. The greater the difference between the 2 surfaces, the more replastering will need doing. Make sure you impress on the builder the need to completely remove all of the “difference”. You want one flat smooth wall, not 2 with a ridge in between.

You will also need a new skirting board. This may have to be quite long. Don’t let him try to put a patch in, it will stick out like a pair of sore thumbs.

What about things that will have to be moved?
Make sure he quotes for repositioning any radiators, switches and electrical sockets. Get him to keep the old skirting boards so everything matches when he makes good at the bottom.

Can we have an arch please?
I hate it when people asked me that. Do you want an actual arch, which begins at skirting level and must be symmetrical and will cost you ….big style. OR, do you just want the 2 top corners rounded off? Go for the corners doing, its easy and simple. Both, by the way, will still require the steel to be fitted.

What about keeping the house clean?
Can he build a dust screen across each room? What state are his cloths in? Most builder’s cloths bring more dust into the house than they prevent from landing on furniture.