Heat loss and air leakage

[Lingwood]

Hi, after some advice on a single property self build (standard block render construction). This bungalow will be 2 bed 6 x10m , I have built much larger extensions to my main house, but I am bewildered what I appear to be asked to do for a much smaller new build?

 

air leakage, heat loss, water usage, tree and ground conditions .

 

are these all required/ the expected? 

[ProDave]

Building regulations have tightened over the years (some would say by not enough) and new houses have to be more energy eficient (no bad thing) so I am afraid you will have to have someone calculate the energy usage, wall insulation etc.

 

Likewise foundations etc, especially if near trees will probably need input from a structural engineer.

 

It might sound like a lot of work when you first look at it, but the result should be you think about what you are doing and end up with a better house.
 

[Lingwood]

I am all for tightening reg, but what I have been suplrised at is what in effect you get away with (legally) with building an extension compared to a single new build.

 

just from my nature, my extensions have been built and insulated etc far above regs for not only long term cost savings but general condition, but I was even shocked at just the drawing price increases as again from my recent extensions which are far more complicated than a new built, just because it is classed as a new build and not an extension. 

 

So, so far my costs are , planning drawings, about £600, planning fee, £385, building regs drawings £500 and bc fee about £600

 

so ontop of this I need to have done , air leakage survey ? Heat loss calcs? Possible tree survey? And ground / soil?????

 

any idea of these extra costs?

[Lingwood]

Actually just a quick Google search of air leakage new build gave me this 

 

http://propertytesting.co.uk/air-tightness-testing-cost/

 

and is saying £200-£300 at most. I was thinking near £1000 for some reasons like everything else is water connect, £1500, gas £700, drop kerb £1500 electricity £1800

 

i had seen air leave testing on programmes like grand designs where they are building passive heating houses and they effectively have to have them sealed like Tupperware boxes and though surely not all houses are like these.

 

 

[Crofter]

As I understand it, all houses need tested, but the actual pass rate you need to achieve is really quite low.

 

I feel your pain with the fixed costs and fees- even though I have managed to avoid a portion of them, it is a much bigger chunk of my budget than it would be for a larger house.

 

Just FYI, my planning fee was £500, road access permit about the same, wate conn £1000, electricity conn £2000. No tree survey.

 

By building a 'portable building' I have avoided BC drawings/fee, SAP, and air leakage test costs. I also did my planning drawings myself.

[PeterW]

In England and Wales you need a DER and TER for a new build - design and target emissions rates. They are then checked at construction and the way to get the air infiltration rate is to use a blower door test. You don't have to do this, you can assume the worst case and then that has a knock on to the final SAP/EPC rating. 

 

This is only is required for new builds - conversions are exempt from a lot of that for some bizarre reason ..!

[ProDave]

1 hour ago, Lingwood said:

i had seen air leave testing on programmes like grand designs where they are building passive heating houses and they effectively have to have them sealed like Tupperware boxes and though surely not all houses are like these.

 

It depends what you want from your house. If mine is sealed like a tupperware box then it meas all the membrane and tape I have used, and attention to detail to get tight joints everywhere will have paid off and I will have a cheap to run house.

 

The point about air tightness, is when you get to a certain level of insulation, then heat loss through the walls becomes very small, and overall heat loss is dominated by ventilation heat loss. If you just build an ordinary house with trickle vents on the windows and no particular effort to seal the fabric of the building, then you have uncontrolled ventilation, and on a windy day it may be too much ventilation and waste a lot of heat.  With a sealed house you ventilate it with an mvhr unit (Mechanical Ventilation with Heat Recovery) so you get a good and constant supply of fresh air, but with most of the heat from the exhaust air put back into the fresh incoming air.

 

Your choice how you build. If it's just for rental it might not be worth going overboard (though it should eliminate damp, condensation and mould issue) but if building it for yourself I would seriously think of building the very best you can.


 

[Crofter]

How much does site exposure play a part in the decision? It's very exposed where I am, and I feel like I am forever opening or shutting the trickle vents. On a breezy day it is too noisy with them open, and also gets very cold. But on calm days the window frames start going mouldy and the house feels very stale, and the windows run with condensation.

 

Going with MVHR on the new house was therefore a fairly easy decision for me. The system is costing well under £1000.

[Jeremy Harris]

9 minutes ago, Crofter said:

How much does site exposure play a part in the decision? It's very exposed where I am, and I feel like I am forever opening or shutting the trickle vents. On a breezy day it is too noisy with them open, and also gets very cold. But on calm days the window frames start going mouldy and the house feels very stale, and the windows run with condensation.

 

Going with MVHR on the new house was therefore a fairly easy decision for me. The system is costing well under £1000.

 

 

Quite a lot!

 

We're the opposite to you, in an extremely sheltered location, and our heating requirement is less than predicted, which I believe is mainly down to not being in an exposed area.  If you're somewhere exposed, then I'd say air leakage and ventilation heat loss probably dominates over all other heat losses, even with just building regs minimum allowable insulation levels.

 

It also depends on the size of the house too.  As houses get bigger, ventilation heat loss becomes a greater proportion of the total heat loss.  Add the two, a big house in an exposed area, and I think achieving a good airtightness result would really pay a big dividend in terms of savings in heating.

[SteamyTea]

Wind speed and direction makes a lot of difference.

If you plot mean temperatures by wind direction you will see what I mean.

As an example I have plotted one years data from the Land's End weather station (as I know it is exposed and not affected much by the land mass).

You can see that when the wind comes from the NE, it is colder than when the wind comes from the South.

This only show part of the problem, as the frequency of wind direction is also important.

NE winds happen 7% of the time, but Southern winds happen 5% of the time (Western is 14% and a mean temp of 11°C).

Then you have to know what mean temperature you need to put the heating on (mine is about 9°C).

And all that is before you take into account windspeed (low speed saps away less heat than high speed) and solar gain (Northerlies tend to cause clear skies)

All good fun and well worth spending a couple of hours on to help work out if your house can be protected from the coldest, darkest and strongest winds that happen the most.