SIDE-RETURN EXTENSIONS – HOW TO BUILD A SIDE RETURN EXTENSION
Updated: Aug 28, 2020
At Draw Plans we create extension plans for all types of homes but adding a simple extension to a Victorian side-return always gives me a buzz.
Victorian terrace side-return extensions are easily one of my favourite types of house extension because the area for development tends to look very small and hardly worthwhile. In most cases it is a strip of space about 1/1.5 metres wide and unless you know what I know you may not fully appreciate just how much an impact a small side-return extension of this type will have on your home.
When it comes to planning, many homeowners mistakenly believe that because it is only a metre or two wide their proposed side-return extension falls within the permitted development legislation. In some cases, they are correct but, in most cases, they are not as you are only allowed to build a side-return extension up to 3 metres long for permitted development. If you wish to build a side-return extension that is more than 3 metres long, then you will need a planning application. Based on experience, almost all the side-return extension plans we create are for extensions more than 3 metres long.
LIGHTWELL – IS IT REALLY NECESSARY TO HAVE A LIGHTWELL?
A lightwell is essential to keep natural light coming into the middle room of the house. Some designers don’t bother with the lightwell and work out a glazed section or roof window in the corner of the new extension roof to give light. We tend to favour the lightwell but again we discuss with the client in the early stages to determine priorities.
BUILDING REGULATIONS DRAWINGS
Before you build anything, you will need building regulations drawings which will specify how you intend to build. For house extensions we usually submit a Full Plans Application to the local building control whilst keeping in mind it can take 8/10 weeks to get the plans passed.
For the structural work we will forward the design plans to one of our engineers to get a structural design plan for the project with structural calculations. These will also be required by building control to pass our plans.
LINE OF JUNCTION PARTY WALL AGREEMENT
When it comes to building a Victorian side-return extension, the last thing you want to do is to put all of the boundary wall on your small strip of land. With space being so important it makes super sense to try to get a “Line of Junction” party wall agreement with the neighbour because if successful that means that you can build astride the boundary line with half the thickness of the wall going on your neighbours land. If that is not possible then you will still need to sort out a regular Party Wall Agreement.
One thing I should mention because most people don’t seem to know is that under the PWA Act you are legally obliged to provide your neighbours with two months’ notice before commencing the build.
So, don’t leave it too late to get your PWA sorted. You can also keep in mind that Draw Plans will be more than happy to hear from you with regard to setting up Party Wall Agreements for your extension.
TRENCH EXCAVATIONS & FOUNDATIONS
The most backbreaking part of the job is the excavations and the average side-return extension will generate about 4/5 cubic metres of soil and mud. I would always advise hand digging for a side-return extension simply because there are usually manholes and gullies within the side return which means clay pipework is underneath the ground that you really don’t want to break.
The standard specification for trench foundations is 1 metre down by 450mm wide. However, if the soil is problematic or there are trees nearby building control may instruct you to go deeper.
Water levels can also be a huge headache as you may hit the water level before you get 1 metre down. If that happens a Terratek Dirty Water Pump for about £60 will get the job done. There are plenty of pumps on the market, but we found this one to be ideal for the job. Just don’t forget to order a waste hose to discharge to the nearest gully and jubilee clips to attach the pipe to the pump when you order.
Once other bit of advice is to make sure you discharge the dirty water to a gully because if you discharge the water into the ground it will find its way back to your trench within a few hours.
Once the foundations are dug out it is time to clear the ground for what will become the floor of your new extension. Ideally, you will need to excavate about 400mm below the existing finished floor levels.
At this point the best way to progress is to clear the site of all excavated material and rubbish. To do this there are a few options available to you including calling a waste removal company or getting a skip license and hiring a skip. Our advice is to always use skips for getting rid of this kind of material as the waste is heavy and the waste disposal companies charge by weight as well as volume. Skips will be far most cost effective.
If you happen to be in a location where it costs and arm and a leg to get a skip license, Hammersmith & Fulham or Kensington Council for example, then consider using a skip wait and load service as the skip driver will give you 40 minutes to fill the skip. If you do opt for a wait and load, then it makes sense to get all the waste bagged up and out the front on the day the skip is due. Otherwise you will need an army of guys to load the skip within the 40 minute time frame.
When the excavations are complete it is essential that building control view the trench before you pour. If you pour concrete without consent from building control you really are going to be in trouble as they will ask you to excavate holes at various points so that they can check the depth of the foundations. You really don’t want to go there so just get the go ahead before you pour.
When it comes to the foundation you have to decide if you are going to mix the concrete or have the concrete delivered and pumped directly into the trench. This is where experience comes into play because many builders still mix the concrete on site and pour where the more experienced and smarter builder will call the concrete company and have the concrete delivered and pumped directly into the trench.
Let’s do the numbers to see how it works out on an average 5 cubic metre of concrete which is 5 of those big jumbo bags of ballast and about 30 bags of cement. Delivered, you would expect a total cost of about £400.
Kerb side delivery means that you have to get the materials into the rear of the property. For that job I would allow a labour cost of £100.
Next comes the mixing. 5 cubic metres is a far bit of sand so I would allow for 1 day with 2 labourers to mix and pour. Cost £200.
A total spend of about £700.
Now if you call a concrete company you will find that a cubic metre of concrete costs around £100 and as you need 5 cubic metres it means that the cost of your concrete is £500.
Unfortunately, the concrete lorry needs a smaller truck with a pump to get the concrete from the front to the rear of the house where the trench is. The smaller truck with the pump and the pipework will cost you £250.
A total spend of £750.
So, there you have it, the pre-mixed concrete route costs £50 more than the direct labour route which is effectively nothing. The biggest difference is not money but on convenience and speed as it will only take a few hours to use ready mix and three to four days to take the direct labour route. Again, from experience, I will always take the ready-mix concrete route.
Do note that if you have any pipework crossing the trench you should bridge with a concrete lintel as you pour. Failure to use a lintel to spread the weight of the concrete over the pipework may cause the pipework to break if you get any settlement or movement.
WALLS – BUILDING UP THE WALLS UP TO ROOF LEVEL
For walls up to the damp proof course (dpc) level I tend to favour engineering bricks rather than any type of block. This is mainly because the foundation slab is rarely level and it will be easier to line up the brick height to ensure I have the correct height when I get to the dpc level. At this point you might also want to consider any opening you need to leave for ventilation pipes to sub floors.
When you have built up to the correct height and you are laying the dpc membrane make sure you cut out some of the old brickwork so that the new dpc overlaps by about 50/75mm.
When it comes to building the walls, it makes financial sense to use 100mm blocks for the outer and inner skin of the boundary wall and bricks for the outer skin of the exposed end walls to ensure they match up with the existing brickwork.
Some builders will buy in reclaimed old stock bricks for the outer skin of the end walls but it doesn’t always makes sense if you are going to be removing a large section of the main house wall which will give you plenty of bricks. I’m not suggesting that you should make the opening just yet and strip out all the brickwork but if you can make a partial opening to get just enough bricks to complete the end walls then it will reduce costs but more importantly the bricks will be an exact match as you are using bricks from the same house for the new brickwork.
STRUCTURAL WORK – STRIPPING OUT & INSTALLING THE STEELWORK
For the uninitiated it can take a little time to work out how to remove the load bearing walls and install steels whilst keeping the upper floors in position. If you haven’t done it before then I would suggest you leave it and get someone with experience to help you with this part of the job.
To install the steelwork it is necessary to strip out parts of the walls but you really do need to know exactly what you are doing here because this work is life changing for all parties if you get it wrong.
Assuming you are building a Victorian side-return extension similar to the plan above the engineer will have specified two sections of steel. One for the main back wall and one for the main side-return wall. Occasionally, if the side return is a long stetch of wall an additional goal post steel may be specified, or underpinning may be required. Just make sure that all the structural work you carry out is as per the specification and plans.
Logically, it is best to install the shorter heavier steel to the end wall first as it will be used to support the steel to the side-return wall. Once the end-wall steel is in place you can remove the remaining supporting brickwork to the side-return wall and install the longest piece of steel. This section of steel will have been prefabricated on one end to bolt up the steel section on the end wall.
Make sure you don’t become complacent at this point and keep your acrow props firmly supporting your steelwork until the padstones have had a few days to dry and that you have filled in the gaps above the steel with slate and cement to ensure a nice tight fit.
Once all the steelwork is installed, the padstones completed and the acrow props removed you can breathe a sigh of relief as the most dangerous part of the job is complete. Now you can get on with stripping out the remainder of the walls and getting ready to put the roof on.
At this point it is usually time to call building control again so that they can have another look around to ensure that the job is going to plan.