It may look good, but did your builder avoid the most common mistakes when creating your home extension?
Error 1 – Excavations and foundations
The first part of the home addition is usually with the foundation and you may be surprised to learn that at least 25% of the foundation is not placed directly under the walls on top. Digging off center or in the wrong position is quite common and in one particular case I had a builder dig for a two room side extension on the wrong side of the line that was installed. His ignorance doubled the cost of the excavations and foundations in the blink of an eye.
Mistake 2 – DPC Waterproofing and Membrane Course
This part of your home extension is a minor but vitally important job. Done wrong, moisture gets into new walls in a matter of weeks and over a year or causes serious moisture problems.
On a site I inspected a few years ago, builders had used plastic debris bags to form a layer of moisture protection instead of using the correct width roll of cpd.
Mistake 3: Extensions are rarely square
The vast majority of house extensions do not have 1 square corner. At least 98% of the builders I have met in the last 30 years had no idea how to check if the extension of the house they were building was in fact square with the property.
Mistake 4 – Floor Services
Time and time again I have come across copper pipes and electrical cables that are laid directly on concrete floors without any type of coating or protection. Copper pipes corrode quickly when directly encased in concrete, as the cement practically eats away at the copper. As for the idea of electrical cables running around concrete without any sleeve, that just makes my hair stand on end.
Error 5 – Windows and doors
You may think this is an easy job, but again, it is quite common that the height of windows and doors are often misunderstood because the floor height was not set correctly or the mason made a mistake. Ideally, all you should see at a garden entrance is the wooden threshold and not a small wall below it. In some cases you don’t even see the sill because the frame was set too low and this too is just poor workmanship.
Mistake 6 – Floor Heights
The new floor heights are amazing in the various ways they can be messed up. Probably the worst case scenario is when they are too tall, which usually results in a step forward of the main house, all because the builder didn’t drop the ground a bit more when building the extension.
Error 7 – Vent to subfloor
When building a side or rear extension on an older property with ventilated subfloors, it is critical that you continue to provide ventilation through the new extension floor. It’s a simple task that costs a fortune, but eight times out of ten the builder doesn’t bother and the end result is usually dry rot within a few years.
Error 8 – Isolation 8
A few years ago extensions were built with little or no insulation. I am happy to say that times have changed and you are now required to have insulation on walls, ceilings and floors. Most councils now insist on additional dry sheathing with insulation-backed board for breeze block walls, so make sure your builder fits. Also make sure they put at least 100mm of insulation on the concrete floors. If you don’t tell them, they won’t bother and building control may not notice.
Error 9 – Drain
This has to be one of the easiest tasks that is invariably done poorly or, in fact, loses as much as possible.
When adding a full-width extension, you should always let rainwater run off the main roof. Time and time again you see this water being allowed to discharge into the extension ceiling, which is simply not supposed to happen as it will always lead to premature problems.
The other point, of course, is that rainwater must not be discharged into soil piles and must have its own means of entering the sewer system or absorbing it. If your constructor gets it wrong, it’s usually a big deal to correct it at a later date.
Error 10 – Invasion
I saved invasion for last mainly because it’s an unfamiliar word to builders and most homeowners, but it can be a huge nightmare if it happens on your building project.
Invasion is where you build on the boundary line. Most people think this is just related to the physical terrain, but in reality, time and time again you see pipes, gutters, and caps clearly encroaching on other properties, which can be a nightmare to correct.
In most cases, the builder carries out the encroachment out of sheer ignorance, but may leave you with a hefty bill to fix or, indeed, legal fees should your neighbors sue you.
Summary
The best way to stay ahead of the game is to stay informed.