Running Costs - Difference Between 2.0 & 0.6?

[lovo]

Hi All

 

We're at the planning stages of our self build, continuing to do our research.  It seems nearly everyone we speak to say they mostly build low energy rather than go near the full passive standard.

 

Anyone got any experience of how much higher heating costs would be in a triple glazed house with say 200mm insulation and a 2.0 airtightness, rather than 300mm and 0.6? I know there are way too many variables to give a definitive answer, but all things being equal would it be 10% more to heat, 25%, 50% etc? Trying to weigh up if it's worth the diminishing returns to go past low-energy and the whole hog to passive. 

 

Many thanks

 

 

[ToughButterCup]

Hello and welcome.

The question you ask is exactly the one I did a few years back.

And the answer is in a program called PHPP, or quicker, cheaper and just as good (probably) is a spreadsheet written by one of our stalwarts @JSHarris

Damn! I've lost it.... not to worry @JSHarris will be along in a minute. And anyway, I'll try and dig it out and attach it later.

 

The PHPP cost me £200, allowed me to play with very many variables, and enabled a common sense compromise. At the moment we are aiming for 19W per square meter rather than the passivhaus standard of 15. Long term, the PHPP program (it's a spreadsheet with a good deal of VB in it) will save me an appreciable amount of money.

[Jeremy Harris]

I've started sticking downloads like this at the top of our website, to make them easier to find.  The heat loss spreadsheet is here: http://www.mayfly.eu/wp-content/uploads/2017/01/Fabric-and-ventilation-heat-loss-calculator-Master.xls .  There are a couple of other tools that may be useful there, too, at the top of this page:  http://www.mayfly.eu/

[Gone West]

Depending on where you live it could be the difference between requiring or not requiring a conventional heating system. My house which is built to PH standards doesn't have conventional space heating because it only requires 1.14kW of heating when -10C outside. I used the PHPP as well, many years ago it cost me £135. The PHPP estimates the house will need 11kwh/m2a and has U factors for the walls, roof and floor of 0.1.

[TerryE]

@lovo, one comment that I will make is that architects seem to love having walls of glass in a house.  Yes, you need glass for passive light into the house.  Yes, glass opens out a room into a view, but I've also seen designs with houses with huge openings onto a row of neighbours' back fences and run-down backs of houses.  So yes, have windows where they work for you and provide positive views, but don't have them just because some architect wants to make a statement.  Just remember:

• Glass loses typically 8x the heat as the same area of wall.
• When the sun shines full-on into a window there's ~1kW/m² of heat incident on the glass surface and may 50% will find its way into your house.  Most passive-class house have more design problems dumping this excess heat than maintaining warmth in the deep winter months.
• If you can see out then your neighbours can usually see in, so maintaining privacy can become a real problem.

Many of us have realised that once you start down the route of building your own house, that it's more an issue of attention to detail and thinking through the design issues to achieve this ~1kW base heating in the depths of winter and have therefore chosen to go down this route.

 

You have to think of the house as a system and balance the components and losses -- for example there's no point in spending a fortune on super U values if you have a house that leaks like a sieve.   Read some of the testimony / blog examples here and use a typical set as a starting point and vary the costs in a balanced way to seek the optimum that you want.

 

The sorts of issues that you might need to factor in are that you might end up spending £50-80K on architects / project manager and other professional fees, and £100K on other trades + materials on top of the core structure.  You need to decide your pace of build and how much are are able / willing to commit, and where you need to spend your hard cash.   For example we chose to split our work between

• a specialist timber-frame (TF) supplier who supplied the slab, TF, insulation and contractually guaranteed air tightness,
• a reputable local builder who did all of the groundworks, drainage, stone skin and slating,
• a reputable specialist window supplier.
• We used the builder's preferred contractors to do the specialist work such as electrics and the slate flooring.
• We decided to do most of the planning submission, all the architectural work, the overall project management, most of the procurement, and most of the internal works ourselves.

This gave us the best value and exactly the house we wanted, but we are both retired and have the time to devote to the build.  This split would have been impossible for us 15 years ago (when we both had work commitments).  Mark Brinkley's House Builder's bible is quite a good intro to some of these trade-offs.

 

[lovo]

Many thanks for all the great info guys, lots more reading and research to do.

 

L.

[gravelld]

On 27/02/2017 at 15:35, lovo said:

 

We're at the planning stages of our self build, continuing to do our research.  It seems nearly everyone we speak to say they mostly build low energy rather than go near the full passive standard.

 

 

One thing that jumps out at me about that is that maybe they say "low energy" because it is vague, while Ph does actually have targets that have to be met. Therefore they can absolve themselves if things don't go right, pushing the risk on to you...

 

Note there are other proper low energy standards, like the AECB Silver. Others may provide other examples. If you don't want to go full Ph you could target those instead, and ask your supplier to meet them or £££.