Block work progressing well

External block work on the left-hand side of the house

For the last four week or so, while we’ve been blogging about what’s happening inside the house, a team have been working outside laying our block external wall.

This wall surrounds the timber frame and protects it as well as providing a base for rendering and cladding.

It’s been progressing well and has nearly reached the top of the first floor windows. This is good news since the windows are currently scheduled for installation starting next week!

Seamless guttering

Aluminium seamless guttering at the back of the house

While we wait for the roof at the front of the house to be completed (pending installation of the skylight), the roof at the back is complete, and we took the opportunity a few days ago to have the guttering installed while the scaffolding is still at the correct height.

We opted for an aluminium “ogee”-style seamless gutter in the same colour as the roof (anthracite). The “ogee”-style simply means that the gutter has a distinctive S-shaped profile at the front to add some detail.

While guttering can be purchased in lengths and attached, we went with a seamless version where the entire length of the gutter is extruded on-site and installed as one piece. This gives both a sharp finish with no joins, and also reduces the chances of leaks through these joins later on.

Once the block work and rendering is complete, we’ll be having square-profile downpipes installed to complement the gutters.

Let there be light

The beginnings of cabling and piping

In addition to our MVHR, there’s also been a lot of work on electical cabling.

Mark Warden from MW Property Solutions started work on the first fix electrics which includes running cabling for all the lights and power sockets, as well as network cabling for the places where we need to plug in devices to access the internet.

It’s not visible in this photo but it’s surprising just how much cabling goes into a new house. Maybe I’ll get a photo of the garage where it all leads and where it currently looks like a telephone exchange!

Adding in our ventilation

MVHR duct in the dining room ceiling

If you’re building a house these days, you can be pretty sure it’s going to be well insulated and pretty airtight.

What this means in practice is that you generally need some way of getting stale air out and fresh air in. One way is using a combination of trickle vents above windows and extractor fans in bathrooms, but a newer way is adding an MVHR (mechanical ventilation and heat recovery) system.

This system has a combination of input and output points around the house, connected by ducting to a central unit. Input points extract air out of rooms such as kitchens and bathrooms, while output points force fresh new air into rooms such as bedrooms and other living areas.

The heat recovery part retains the heat inside the house by extracting it from the stale air and using it to heat the fresh air as it comes in. This part can be bypassed in summer when the fresh air is already warm.

We’re now in the process of having the ducting fitted, which is the first service generally to be fitting inside the ceiling, followed by water pipes and electric cables. The ducting is a new, flat style which leaves more room for other services and insulation, and each input/output point has a short, flexible foil section eventually leading to a discreet vent in the finished ceiling.

Insulating the loft

PIR insulation panels installed in the first floor ceiling

Our house has been designed with the “cold roof” – that is, the loft space is intended to not be heated and be used as a storage space rather than a heated area that could be a room.

Since it’s a “cold roof”, the part we need to insulate is its floor (or the first floor ceiling) so we can keep the heat inside the main house and out of the loft. In many existing houses, this would be done using rolls of mineral wool or maybe blown insulation.

However, since we have a new build in quite an exposed area, we need to go one step further to ensure we have an energy efficient house that also has a usable loft space – that means installting rigid insulation panels (also known as PIR). These panels are roughly twice as efficient as mineral wool, and so you only need half the thickness for the same effect.

In our case, our ceiling joists are 100mm thick, so we started off with 100mm thick insulation panels, cut to fit between the joists. The carpenter had already installed ceiling battens to fit the plasterboard on to, which keep the insulation in place, but also make it a lot harder to get it in place to start with (especially when combined with timbers running across the top of the joists which act to “sandwich” the insulation in between)!

At this point, we’ve stopped to allow the plumbers to install our MVHR system (which will be running partially in the loft). After this, we will overlay 100mm of mineral wool on top. This will allow the insulation to run over and around the MVHR ducts as well as in all the intricate gaps between and around the roof trusses. Once this is then boarded over to provide a stable platform, we’ll have our finished loft space.

More underfloor heating

Underfloor heating pipes clipped to the underside of the first floor

Now that our screed floor is dry enough to stand on, plumbing work has recommenced with the installation of the underfloor heating for the first floor.

Unlike the ground floor where the pipes are encased in the screed, we’ll be carpeting most of the first floor. Therefore, the underfloor heating pipes are weaved through the joists and clipped to the underside of the wood floor boards.

Underfloor heating manifold

Like the ground floor, there is a separate manifold on the first floor where all the pipes terminate. Eventually, this will be connected to the boiler to distribute hot water and heat the various parts of the first floor.

Our house is a swimming pool

Liquid screed just laid

Today’s been an exciting day! The team from Smoothflow Liquid Screeding arrived in the morning to prepare the floor and make sure everything was ready.

Once they’d calculated how much screed they needed, they made the phone call to the supplier and only a couple of hours later, we had a screeded floor!

Liquid screed arriving on a truck, with the pump in the foreground

The house currently looks like a swimming pool, but the hairline cracks show it’s starting to dry. It will take up to three months or so for the screed to completely dry and be ready for flooring, but within a couple days we’ll be able to walk on it.

Next up, the plumbing team will be back to start work on the underfloor heating for the first floor.

Ground floor underfloor heating is in

Underfloor heating pipes laid and clipped

The days are passing by quickly and since the last post, the ground floor is now ready for screeding.

Once we finished laying the membrane and expansion strip, Matty Beecher from MSB Heating Solutions and his team visited to install the underfloor heating. This is basically loops of plastic pipe clipped to the insulation.

Underfloor heating manifold

The loops all make their way back to the manifold. This is a device that controls the hot water to each loop and regulates the overall temperature of each zone.

This is the final step before the screed is laid tomorrow.

Preparing the ground floor

Installing the radon barrier/damp-proof membrane

Now that the roof is mostly complete, it’s time for us to move on to inside the house. Over the past few days, we’ve been preparing for a special date – the day the liquid screed is poured to provide our solid concrete floor which we’ll then finish right at the end.

The step before the first step was to make sure our block and beam floor was clean and flat enough for the next steps. We used a combination of an axe to chip away at any raised bits, and our trusty site vacuum cleaner James to clear away debris and sawdust.

Once that was done, we moved onto the first step – the radon barrier and damp-proof membrane. Since we’re in Cornwall and radon gas in the ground is a recognised issue here, all new houses need to have a radon membrane installed on the ground floor. This stops the gas rising from the ground and into the house. A damp-proof membrane is also needed to stop damp from rising through the floor. We found a two-in-one membrane that handles both and installed that – that’s the yellow sheeting in the photo. All the seams need to be overlapped, taped with double-sided tape and then sealed with duct tape. The membrane is taped to the damp-proof course running around all the walls (in black), so that any gas underneath the membrane can escape out of the building.

Structural grout underneath a steel beam

Of course, nothing is ever simple, so before we went ahead to the next step, we needed to make sure the steel beams were secured. They come attached to the floor with some bolts, but other than that and maybe some plastic packers, there’s a gap between the bottom of the beam and the floor. To make sure the beams are well supported, our carpenter fitted some simple formwork around them, and we filled it up with a structural grout, which looks a lot like sloppy concrete. It dries pretty quickly, however, and provides a strong support base escasing the base of the beam.

Rigid insulation and a black membrane ready for the next step

Once that was all done, we were ready for the next step – insulation! We have 150mm of rigid insulation boards across the ground floor to keep the heat in and provide a base for our underfloor heating.

These boards come in large sizes but can be cut easily with a handsaw and are relatively light.

In the middle of the photo you can see a conduit with a cable sticking out, and this is also visible in the first photo. This one is for a floor socket and so we needed those to be in place first. The bottom of the insulation board was then cut out to slot nicely over the conduit, and any gaps filled with expanding foam. The boards are staggered and nicely butted up to each other to provide a continuous base.

After this comes the last of our layers – the black membrane. This is very similar to the radon barrier/DPM, but it provides a sealed surface for the liquid screed to be poured into so it doesn’t leak and escape – therefore it’s very important that any holes are patched up. We laid it with overlaps just like the radon barrier and taped the seams and edges with duct tape, making sure there were no gaps. Finally, we laid a strip of edge foam around the perimeter, stapled to the timber frame. This foam provides space for the screed floor to expand and contract as it heats and cools.

We worked pretty hard into the night to make sure it was all ready for the next step – our underfloor heating, which I’ll write about in my next post.