Sewage treatment

Although the main pipe that goes from Perranporth to the sewage treatment plant by Cligga goes past the front of the house, that is under pressure and isn’t a pipe we can discharge into.

At the moment Silver Spray is a soakaway !

So, as the house is being “upgraded” we’ll be fitting an on-site sewage treatment plant. These treat the toilet waste and to a level where the water meets the rules to be discharged into the groundwater.

This is what the neighbouring properties all have.

Next door to the east, Ramoth have a Klargester BA 450 BioDisc (now part of Kingspan Environmental) unit, that was installed by Dorset based Environmental Drain Services Ltd.

Talking to Environmental Drain Services:

  1. As it’s a treatment plant and not a septic tank the 7m minimum distance from a habitable dwelling rule does not apply.
  2. You need to be able to, on-going, access the lid to get into it. So you can build decking etc over it, but you can’t stand, drive or put earth over it.
  3. We should be able to rely on the percolation test / survey done for Ramoth way, as this is just next door. It’d be very unlucky for this to not be indicative of the Silver Spray ground.
Talking to Mark at Ramoth, there is not only the Klargester unit, with it’s small power supply, but the outlet feeds into a series of underground trenches, that in their case are closer to the house than the Klargester. These trenches are rock filled to help the distribution of the discharged treated water.


SAP calculations (Air leakage, U-values & thermal bridging)

As we head towards sending in the planning permission (we’ve had 2 positive pre-planning meetings), the design has been sent for a preliminary SAP analysis.

A fundamental objective is to create a thermally efficient building, so that over it’s lifetime, the amount of energy to keep the interior at a comfortable temperature and humidity more than offsets the cost (money and environmental cost) to achieve this efficiency.

In crude financial terms, the cost of heating an uninsulated house is nearly three times that of heating a modern well insulated property of the same living area.

Heated buildings loose energy in 3 ways:

  1. Air leakage through holes (hence an airtest and an “air-tight” building).
  2. Through the fabric of the building. The u-values of the materials measure how much heat is lost through them. This is primarily the walls, floors, windows, doors and roof of the building.
    The lower the U-value, the better that section of the structure. For example, a wall with a U-value of 1.0 will lose heat twice as fast as a wall with a U-value of 0.5.
  3. Through the cold bridges between the different elements. These are the Ψ (psi) values.
    – “Thermal bridging occurs where the insulation layer is penetrated by a material with a relatively high thermal conductivity.”

The SAP assessor will look at all of these. They will multiply the Ψ (psi) values by the total length of their construction in the building to get a y-value. The y-value is analogous to an aggregated u-value for all the junctions in the building.

What y-values are used in the SAP calculations can have a big impact on the end figure.


  1. SAP assessor can use default value of 0.15, or
  2. Calculated value using the Ψ (psi) values listed by the Building Regulations for Accredited Details (normally 0.8 or higher, or
  3. A calculated value using thermally modelled junction Ψ (psi) values, which can come out as low as 0.04 depending upon construction details used.
The difference can, apparently be the equivalent of an open garage door on the side of the building ! (best to worst).

Contractor Contracts

An email in from a buddy who has managed quite a few commercial and larger (multi dwelling) building projects:

The only other things to be aware of and concerned by is the type of building contract to be used. The standard form JCT contracts, I believe, are biased towards the contactor, the ACA standard form was written by Architects and is more balanced.

You also need to think about the level of damages for overrun on the contract. This is slightly more complicated than it might appear. One of the most crucial decisions made by the contract administrator is the issue of the Practical Completion Certificate as this signals the contract has been satisfied.

If there is an overrun, as invariably there is, he has to decide who is at fault and you are in the territory of the famed “critical path”, ie if the delay prevents progress on the rest of the build its on the critical path and who ever caused that delay in culpable. The reason these decisions are important, even for one week is there is a swing for every week by approximately twice the level of damages assuming damages are set at a level similar to the “preliminaries” figure. Prelims are the costs to the contractor of being on site, ie his admin costs. So if damages are say £2000 pw and prelims say £1500pw and there is just one week delay caused by the contractor he is £3500 down. You get the picture it can get very prickly.

Good luck, I am sure it will go well, new builds tend to be easier, provided they are well planned, because there are less unknowns. Keep an eye on any unusual materials and/or bespoke items that have long delivery lead in times and/or are coming from none standard sources as these can be the source of serious delays.

Project Management

A nice article by Charlie Laing on Project Management at:

They talk about a  Joint Contracts Tribunal (JCT) contract between builder(s) and client. Going through it and both signing it, so that there is a pre established way to control the work and exchange of money that is fair to all.

For changes during the project, their advice is that:

  • contract changes can only be made by the project manager / contract administrator (which should not be the client).
  • the builder should quote for the changes
  • the contract manager uses this to get client approval. If given, passes this on to the builder.

As I’ve read elsewhere, informal approval changes from the client is the most common area for problems when the consequent bill for this arrives.

A Joint Contracts Tribunal (JCT) contract, brings with it an agreed adjudication / arbitration route, but in most cases, a common sense, sit down and come to an agreement solution is best. Here the contract manager can mediate.

For this, Charlie Laing have some suggested questions to cover the conversation over what is being claimed. Is / was it:

  • described within the contract?
  • described as a revision to the contract and the contract sum?
    – if yes, was it requested, quoted for and approved?
  • related to completed work? Is there any evidence that it has been done?
  • related to work that the contractor had to redo through no fault of his own?
  • requested directly by the client?
  • raised by the contractor to the client directly as an option that they may choose?
  • clearly confirmed by the contractor to the client as being at extra cost?
  • carried out with an element of risk by the contractor through not following procedure?
  • in line with market rates for materials and labour time used
  • related to the actual labour time used

In light of the answers to the above, is full payment of the claim considered fair and reasonable?

This all re-enforces the idea I’ve read elsewhere abut keeping a site / project diary. ie keeping your own notes and other records.


The Natural Home – Ecobuilding Consultancy

It was a while ago, that I met up with Adam & Sarah from The Natural Home, Ecobuilding Consultancy.

It was great to get input from a team that don’t have a vested interest with a particular main project supplier, such as the architects or builders.

Amongst their many comments and recommendations:

  • If you find a contractor you trust, they’d recommend their employment under a ‘prime cost’ (also know as ‘cost-plus’) contract. This means the contractor charges for the total price of buying goods, materials and components, of using or hiring plant and of employing labour, in order to delivery the construction project plus a management fee.
    Their are apparently a broad range of contracts available and they could advice / assist with this.
  • Adam pointed out that the distance from the proposed house to the garage at the front may need advance consideration in relation to the surface water run-off  from the building and soak-away. This / these have to be at least 5 meters from the building, so may need to go beneath the garage.
    Adam recommended a permeability test to ensure a soak-away can accommodate the volume of discharge.
  • Current building re-use. As clearing the current building will give a large amount of aggregate, Adam suggested that it might be possible to crush and use some of this in the concrete mix for retaining wall sections.

Second pre-app meeting with Cornwall Council

Today, Robert (the architect) and I had our second pre application meeting with Cornwall Council.

The first pre-app was great. We felt the verbal meeting and post meeting written response were both very positive. They wanted some tweaks / work done on 2 small areas. The first was more that we hadn’t covered that we were making all the considerations we should. We did have it all covered, but this was written up in the pre-application we made. The second was that they felt we could change the treatment of one of the areas to visually improve it.

So this second pre-app was to go over our submitted suggestions and ideas. The planning officer had a preferred option, which, in our view, looks great and lets us crack on with finalising plans.

The next step is to run the general scheme past a few potential builders, and probably a structural engineer and probably a Quantity Surveyor (QS) so that we can confirm it’s all feasible to build and that the budget is sufficient for the current plans and ideas.

Comments on some (great) work by Lilly Lewarne

I met Chris Richards, from at a sustainable housing evenign at the Eden Project. He has since sent over some of their recent work, that I personally liked.

They look to have good eco / sustainable experience.  Not least of all being involved with the Fairglen Eco Community.

The project that had the most info and closest relationship to Silver Spray is “Salthouse”.


I like what I presume is the main entrance. Wood flanked by glass. I like the linear “journey” from the rear parking down to this door.

Looks like a great view from the lounge !
– I like the big solid looking doors.

What to do, with who ????

I’ve got a shortlist of 4 companies to work with for this project.

Each have now met with me, some more than once. Each have seen the site. Each have gone over my folder of ideas that range from my sketches to look and feel pictures. They’ve also all looked at this site.

Each have come back with varying costs to come up with initial ideas (sketches) and to use those to come up with project costings.

To help them with this, the site survey for levels etc. is being commissioned.

Cornwall based Eco House have built some stunning local projects. As with all 4 companies, I liked the feel of the meetings and chats we have had to date. They are charging a sub £1,000 fee (+VAT) to come up with initial ideas and costings for the project. They report a cost of  £2,000 /m2 for a full design, and build.

Facit Homes have come back with the most detailed initial proposal on how they would come up with sketches etc. Of the 4, it is also the most expensive, but it would give more than the others are suggesting in terms of taking ideas further. The proposal would be enough for an initial consultation with the local planning authority. It does seem that their construction method(s) would have the lowest construction environmental impact. Talking to them, their properties tend to cost £1,700 to £2,000 per sq metre.

Hanse House are charging less than Eco House and will have 2 of them spend the day with me next week. From that they’ll come up with their sketches and costings. They say that excluding foundations their houses with everything except the kitchens (ie incl light switches, paint, floors, bathrooms etc.) they tend to cost around £1,400 psm (per sq metre).

  • When I visited a Hanse House in construction, I was put off by the level of polystyrene, foam guns etc. in the materials. They have a great reputation for the end product energy efficiency, but I’m not comfortable with their decisions on construction materials.
  • Construction (embodied) Energy Vs Operational Energy

Potton are also waiting for the site survey and are then going to come back with initial sketches etc. and costings based on that. They say that their houses tend to come in with everything for around £1,250 psm

It’s an interesting period of almost 2 many choices that seem to fit into 4 categories:

  • Layout and design.
  • Environmental impact of the build process.
  • Ongoing environmental impact of the house once it is up and “running”.
  • Cost of these aspects.