Solar P.V. installation

Why install solar p.v.

Up until the begining of this year it was pretty much a no brainer to install solar p.v. on a house, particularly a new build if you could afford the initial outlay as the Governments Feed in Tariff paid good money for power generated regardless of you using it yourself. That all changed this year as the F.I.T. payment dropped to 3.9 pence per kwh, making any payment for generation only a few hundred pounds a year at best.

I did consider dropping any solar p.v. installation but felt that overall it was still a worthwhile thing to do.

Now that there is no money to be made from a solar p.v. investment, actually using the electricity at source becomes more of a priority. This is not as easy as it sounds as generally you want electricity at times of the day when none is being generated. I will be diverting excess power to an immersion heater to heat my hot water, which should provide pretty much all of my hot water needs for half of the year. It is also possible to use timer delays on high consumption appliances such as washing machines and dish washers so they come on in the middle of the day. And as I work from home my energy use during the day for computers, lighting etc should be covered.

Another cost saving on installation is the cost of roof tiles. I chose to use an integrated roof system that fits flush with the tiles rather than mounted on top of them, saving just over £1000 in tiles alone. The solar panels themselves are all black with black trim and no visible silver lines across them so should be as discreet as is possible on the roof. The area of roof where they are mounted is directly south facing and on the rear of the house, so not visible at all from the road.

Power storage is often mentioned, especially by solar companies trying to up-sell, but the reality is that at the moment there is no financial justification for installing batteries. This may change in the future but it seems a long way off.

My planning permission came with a condition to generate 10% of the energy consumed by the house on site. The planners agreed in principal that they would drop this as I was building a house with such a low energy requirement, but I decided to go ahead anyway.

If I was only going to live in the house for a short time the cost of solar really wouldn’t stack up, but as I am her for the long term it will hopefully be a sensible use of a few thousand pounds.Installing flashings to bottom edge of panels

Plastic support panels fixed to battens

Flashings around panels

Flashings around panels

Installation completed

Solar array set into tiled roof


Fixing roofing felt

Fixing roofing felt

Nailing roofing battens


Tiles loaded on roof

Lead work to box gutter

Tiling the valley


Fitting roof lights

Pointing the ridge

Tiles around flush P.V. panels

Fiberglass balcony and box gutter

Balcony covered in OSB before fibreglassing

Timber frame wall panels

Ground floor

Ground floor wall panels

Crane lifting panels

Fixing steel post

Ground floor wall panels

Fixing base of corner post

Fixing ground steel floor beams

Ground floor steel beams ready to start fixing joists

Floor joists over ground floor panels

Metal web joists over living space

Air tight membrane over joist ends

The guys at MBC started fitting airtight membrane and tape right from the start of the frame erection as this is the only way to get a really airtight house. It is too late to try and block up holes and cranks once the frame as been erected, which is the method used by most builders. Before the joists were fitted an airtight membrane was taped to the top of the ground floor walls and wrapped over the end of the joists to be taped to the inside of the first floor walls.Steel beam junction

One of the critical elements of a passive house is not to have thermal bridging of the insulated layer. All steel work is kept to the inside leaf of the frame, allowing good coverage of insulation around steel and keeping it on the warm side of the build.

First floor

First floor wall panels

Lifting first floor steels


Roof trusses being lifted

Roof trusses being installed

Roof topped out

Timber frame arrives on site

The first delivery of the passive timber frame from MBC Timber Frame Ltd arrived this morning from the factory in Ireland. The access to site is quite tight so MBC had arranged to have their truck met by a smaller vehicle and transfer the load a couple of miles away so it would not block the road. The smaller vehicle was still actually pretty large and managed to take the load in just two trips, but with a fairly hair raising few moments each time trying to fit through the gates. The drive has pillars either side of the gate and is also not level. We had to use planks to raise the low side of the truck to level it off to allow it to drive through, still with only an inch or two either side.

Transferring the first load

First delivery arriving

Squeezing through the gate

Unloading wall panels

Panels stacked on the slab

Setting out sole plate

Setting out sole plate

Positioning sole plate and damp proof course

Drilling fixings for sole plate

Before the timber frame wall panels can be fixed in place a timber sole plate is fixed down to the slab over a plastic damp proof membrane (dpc) strip. The sole plate must be accurately set out as the walls will follow its line around the building. It gives a secure fixing point for the wall panels and the dpc prevents any damp rising up into the wall.

Pouring the insulated raft

Loading the pump

Adjusting the boom to reach the back of the slab

Raking out the concrete

Vibrating poker to help the concrete flow and fill all gaps

Checking  the levels with a laser level

Tamping down concrete

Using a bull float to level the slab

[/fuForming the recessed shower tray

Power floating the slab

Finished raft ready for scaffolding and timber frame

Passive slab foundation

A passive slab foundation is a raft that is fully insulated from contact with the ground below eliminating any thermal bridging. Insulation forms the shuttering for a concrete pour, and layering of the insulation allows a ring beam to be formed around the perimeter and thickening under load bearing internal walls. Reinforcing steel is added to the raft according to calculations from a structural engineer to ensure all loadings and ground conditions are accounted for. Due to the raft having a very large surface area compared to traditional strip foundations, the load at any given point under the house is much lower. The structural engineer needs to design the raft to suit ground conditions, which is why a full ground bearing test and soil analysis was undertaken at the start of the project.

Levelling the sand blinding

The stone sub base is laid and compacted to within a 20mm tolerance. A sand blinding layer is then laid and compacted to a 5mm tolerance as a base for the insulated slab.Laying drainage runs

Once the blinding is levelled and compacted the drainage runs and ducts for incoming services are dug and laid. All of the drainage runs are pressure tested by bunging the lower end of the pipe and filling with water, any leaks will show up with a drop in level. It is critical to plan in advance where all drains and ducts and services are going to run in the build as it is not possible to add them at a later date. It is far better to have services coming through the slab in a controlled manner than try and make holes through the walls at a later date as these are much harder to keep an air tight seal on. Drainage should not penetrate through external walls or roof for vented stacks as these will create a large thermal bridge, not only reducing efficiency, but increasing the chance of causing damp patches around the thermal bridge.

Perimeter insulation and drainage

Perimeter insulation set out

First layer of insulation down

Further insulation laid over damp proof membrane

Once the perimeter insulation was set out the remaining internal area was filled with a 100mm layer of insulation. A damp proof layer/Radon barrier was then laid over this and taped together to form a huge red paddling pool. A further 200mm of insulation was then laid on top of this, leaving a gap around the edge for the steel ring beam and also gaps where the structural internal walls would be located. This would allow a thickening in the concrete raft when it is finally poured.

Steel ring beam

Bottom layer of steel mesh over insulation

First layer of steel mesh laid over insulation

All had been going so well but a couple of ‘elastic tape measure’ moments by the ground workers had put a duct and soil stack in slightly the wrong place. Fortunately spotted before the concrete was poured and easily fixed, but a major disaster to have a duct coming up in the middle of the living room. A variation of the old measure twice cut once and just showed how important it is to check and re-check things that cannot be changed later.

Under floor heating pipes over bottom mesh

Laying the top mesh over the ufh pipes

I could have laid the under floor heating pipes myself as it is really not a tricky job, but decided as there was only one of me, and its a job made much easier by at least two I would leave it to the guys laying the slab. They made pretty short work of it and all eight runs were finished in half a day. I decided to relay the last couple of meters of all the pipes myself as they had not been aligned with the ports on the manifold very well. The connections to the manifold are really fussy about being square and straight, and the effort was worth it to enable neat connections. Whilst connecting the pipes to the manifold I managed to mislay an olive. After spending a morning visiting every plumbers merchant locally to find a replacement with no luck I decided to fabricate one so I could get the pressure test completed. It was a pretty straight forward job purging all the air out of the pipes, and then left the hose running to build up the pressure. I left the system at 4 bar for a few minutes with no loss of pressure, so all good. The system will be left at 2 bar during the concrete pour so any damage to the pipes can be  spotted straight away, although I think it is unlikely as the pipes are pretty tough.

Under floor heating manifoldPressure test

Slab ready for the concrete pour

Oversite and drainage

Site cleared and levels reduced

nspection chambers set to level

Rodding point for surface water drainage

With the reduced dig and drainage runs complete the site is covered in free draining stone compacted in layers. This provides a base for the raft foundation to sit on.

Checking the levels of the sub base

Compacting stone in layers with vibrating roller

Lucas made the most of his inset day by coming to site to watch the diggers. He got some handy tips on how to lean on a shovel and drink tea, and also try out the digger and roller.

The first set of groundwork contractors job done, leaving a really tidy site ready for the slab crew from MBC Timber Frame and their ‘Passive slab’

Moving utility connections

Before the house can be demolished all of the utility services (Gas, Electricity, Water) need to be disconnected. Rather than pay for a disconnection and then again for a new connection later I decided to move them to the side of the garage so they would be out of the way. I would then run my new gas and power connections from these into the new house at a later date and be able to have a builders supply of power and water during the build.

The first job was to locate the incoming services under the front garden so they could be redirected. The power and water were easy enough but for some strange reason the gas went off in another direction so took a little longer to find.

The power cable is cut and fitted to a new cable running to the garage. This is done whilst still live with only a steady hand, some plastic wedges and leather gloves for protection.

Ground bearing test and soil analysis

A requirement of the foundation design for the house is to establish the soil type and bearing capacity of it to allow the structural engineer to design a suitable slab and sub base for it. A small rig was brought to site to undertake a ground bearing test by driving a hole into the ground down to 4 meters, and to also bring samples of the soil up to the surface for visual inspection and collection for lab testing.

Operating the mini piling rig

I was fully expecting to find rock chalk at about 1.5 meters as this is what we have at the top of the garden. I came as quite a surprise to find silty chalk with blue clay beneath it. Our plot is at the bottom of the valley where sediment must have formed.

Core sample from below groundDivining for underground cables

It came as quite a shock to see bent coat hangers being used to check for underground cables and pipes. I am not sure I would rely on it 100% but he did find my underground mains power cable and also water connection to the house.