What Does an Architect Check when Building An Extension?
When we run a job on site we carry out lots of site inspections, whether it is building an extension or renovating a house. The idea is to check that the work is being done correctly and that there are no problems.
Even a small extension is relatively complex and there are lots of things to check. The trick to doing this well is to be clear about what you are looking for on each visit. We work through a checklist of more than 100 items on every project, looking at each one at the right time in the build.
Some of these, such as safety, are critical to the success of the project and we will check them every time we visit. Others, such as the foundations, or the DPC, need to be checked at exactly the right time before they are covered up.
I Don’t Have an Architect, What Should I Look Out For on Site?
First you should really consider getting an architect. Check with the RIBA for a local practice, or give us a call and we will help you. But if you are really happy in dealing with the builder yourself then here are 10 of the most important things to look for on site, and our tips for how to make it work!
1 Site Safety
The work area should be separated off from the rest of the house to prevent accidents. No one other than the builder should be able to go on to the site without checking-in first.
It’s good practice to put 2.4m high hoarding with a lockable gate to the street front to help keep the site secure. It’s helpful for the builder to display a sign board on the hoarding, showing their name and telephone number. Most neighbours will find this reassuring, and it helps to show that the builder is taking responsibility for site safety.
We ask all our sites to be registered with the Considerate Constructors Scheme. This gives added reassurance that the builder will follow best practice, and that the site will be safe.
2 Only Use Good Builders
No doubt the building firm will have been chosen very carefully. Now the build depends on the workers on site. There should be a clear hierarchy, with a good foreman in charge of the work.
Each of the workers should be skilled in the type of work they are doing. The foreman should have copies of their Construction Skills Certification Scheme (CSCS) cards. It’s good policy to wear a hard hat, high vis jacket and safety boots at all times on site. A well prepared and workmanlike approach goes a long way towards a successful build.
There are some red lines. Anyone ignoring health and safety, smoking, or taking drugs or alcohol should not be allowed to remain on site.
3 Are The Drawings On Site?
You’d think this was obvious – but it’s worth checking. It’s amazing otherwise how many mistakes can be made by not looking at the drawings and spec properly.
At the early stages on site we check that the foreman has got a full set of the drawings on hand in the site office. These should be referred to frequently, so if they don’t look well-thumbed then something’s up.
Once the project moves on to the finishing stages then it is good to see copies of the drawings taped to the walls inside every room. This makes it easy to refer to them. Details such as the exact tiling layout or position of lights can only be got right by working to the drawings.
4 Foundations Depth
It’s good to check that the foundations have been dug out to a deep enough level. This will be shown on the engineer’s drawing but usually will be at least 1.5m below ground.
This is a stage that Building Control will need to check too, so the builder should call them to let them know, before they pour the concrete.
If there are tree roots in the excavations, then it can be necessary to go a bit deeper. If possible it’s good to take photographs of the trench, with a tape measure in shot to show the depth.
5 DPC Height
The DPC or Damp Proof Course is what stops water getting in to the finished extension. It needs to be 150mm above the external ground level.
This is quite simple, but there can be so much digging during the work that it can be tough for the builder to accurately gauge the external ground level. This is something to check, to make sure they do not make a mistake, as it is not easy to correct later.
It is good to use engineering bricks which are impervious to water, to build the walls below DPC level. This also helps to show clearly where the DPC will be. If the external ground level is being raised with a new patio, then the DPC will need to be 150mm above the new level.
6 Setting Out
The drawings will show the key setting out dimensions, and the builder will then set out the work on site.
Often they will use chalk or guide lines for this, so that it can be seen on site before the work is started. This is a good time to walk through the site together checking that the critical dimensions are right.
A bit of extra time checking the measurements at this stage is well spent. It’s no fun asking a builder to move a wall after it’s finished.
7 Are The Right Materials Being Used?
The technical drawings and spec will detail the materials to be used for every part of the project. These will have been well planned and thought through, so it’s important that the builder keeps to the spec.
We always check that the right materials are on site for the work, and if anything is wrong we will get the builder to change it. It’s often just an honest mistake by a supplier that the builder will be happy to put right.
The builder should keep delivery notes of all their materials which can be looked at, if needed, to confirm they are correct.
8 Is The Site Dry?
It’s natural that when the digging and foundations are being done the site will be open and might get wet. But once the build starts to move on and the walls are up it needs to be kept dry.
Internal timber should not be wet, as it can warp. Concrete, screed and plaster need to dry out before the work can be finished. Electrics and water don’t mix, so this is important.
The builder needs to protect the interior from rain until the build is finished and watertight. This could be with plastic sheeting, or in some cases a temporary metal roof. We like to check the plan for this early on, to make sure that this will be done well.
9 Test Lighting And Heating Early
Lighting and heating are installed in two stages. At First Fix the cables or heating pipes and the main hardware are installed but not finished. At Second Fix the switches, light fixtures and radiators are installed and the work is finished.
It makes sense to check the work at First Fix, to make sure everything is right. It’s easy to move a light point, switch or radiator at this stage, but much more difficult after Second Fix.
It is also good to make sure the builder makes technical checks of the work at First Fix, such as pressure testing under floor heating pipes, before laying the floor.
10 Flood The Roof!
Once the roof is finished we like to make sure that there are no leaks by getting the builder to run a hose on it for a couple of hours. This simulates a heavy storm and is a good chance to check that all the gutters and rain water pipes are flowing smoothly too.
A small leak in the roof can cause big damage over time, so making sure that it is completely watertight is well worth it.
Finally, Take Photos!
Our final tip is to take lots of photos during the build, and keep them in dated folders. You can’t have too many photos. We take thousands on a typical extension. They’re a great reference, as well as being fascinating to look back on when the build is complete.Contact 2PM Architects
More Guidance On Building An Extension By 2PM Architects