Timber frame new build

Threebesties

Hi all,
I am starting a new build via a building contractor and have decided to go with timber frame. Our builder is suggesting we go with 184mm studs where 140mm seems to be standard. Would appreciate people's opinions/advice. 140mm will achieve a u value of 0.215 where 184mm will achieve u value of 0.17. Is this upgrade worth an additional €2k?

Gumbo

Who is supplying the timber frame kit?
What do they recommend?

I would always advise build as good as you can at the start as you cannot change that later.

delfagio

I would definitely recommend going the extra for u-value purposes, as it's very hard if not impossible to change things later. Best to get off to the best start you can.

As mentioned I would speak to the timber frame company as this could have an impact effect of later stages, structural elements etc.

Make sure airtightness is addressed also.

Threebesties

Thanks for comments guys. This is where my concern of potential bias comes from.. The builder also supplies the timber frame so going with 184mm equals more profit for him. Any other quotes we received in the tender stage quoted for 140mm as standard.

Rabbo

The maximum wall u value for a new build is 0.21. This almost invariable has to be reduced further to achieve overall energy targets in a new house.cis this an extension or a complete new house? If it's a new house, you need to get a prelim BER and specification prepared first in order to ascertain the specification required for your house to comply. Do you not have an Assigned Certifier appointed?

galwaytt

In the absence of an airtightness target you might not get value in the thicker frame. And don't let the builder pick it.

Threebesties

The house complies with Regs (preliminary BER A3) at 140mm and airtightness expected <1. I am wondering whether it is worth the upgrade to 184mm from point of view of comfort and energy bills.. Thanks

npgallag

I am also starting a timber frame new build shorty and spec of external wall is 140mm with 50mm insulated plasterboard giving u-value of 0.15. So upgraded plasterboard might be option. Also airtightness will be < 2ACH... are you going for < 1..?

galwaytt

..what I always say to people on the u-value cost vs airtightness question is this: increasing the u-value increases costs directly, as it is a reflection of materials used.

Airtightness on the other hand, may not. By which I mean, airtightness is a measure of quality-of-build - of workmanship.

Therefore increasing u-value (on paper) is not necessarily beneficial on it's own, whereas increasing airtightness most assuredly is.

A good house built to 0.21 and with an airtightness of say 0.8 is going to be better than a house with a u-value of 0.16 and poorer airtightness.

Once below 0.20 imho, airtightness overtakes u-value in measurable benefit.

Threebesties

Thanks @npgallag.. I might put that suggestion to the builder to see what additional cost is involved. Yes going for air tightness of <1. I am interested to know what ventilation system you have chosen? We can't decide between demand controlled MEV or MVHR.. Pros and cons to both so hard to chose.

Thanks @galwaytt, that's a very valid point you make. My question is this- if going for excellent air tight value, do you need to match that quality as such with low u value windows etc, ie. If we went with double glazing with u value of 1.4, would we be creating a weak spot and would this be a foolish move?

Calahonda52

Threebesties wrote: »

I am interested to know what ventilation system you have chosen? We can't decide between demand controlled MEV or MVHR.. Pros and cons to both so hard to chose.

Would you care to pens few lines on the pros and cons of each as you see them?

IMO its clearcut: it is much better to go for ......like X Factor, back after these...:)

Threebesties wrote: »

Thanks @galwaytt, that's a very valid point you make. My question is this- if going for excellent air tight value, do you need to match that quality as such with low u value windows etc, ie. If we went with double glazing with u value of 1.4, would we be creating a weak spot and would this be a foolish move?

Heat is lost in 3 ways:
Conduction, convection and radiation.

The convection route is the one when you have excess air loss so get the A/T down and u reduce convection losses.
You are losing the heated air.

Conduction is reduced by using good insulation and careful design so as no cold bridges.

radiation losses occur primarily through the glass in windows so in theory 3G is better than 2G but then on south facing, 3 G reduces solar gain during winter

Threebesties

As I see it, Mvhr has the added benefit of recovering the heat from the extract air warming up the cooler incoming air. Great in the winter for sure but do you want this in the summer when you have lots of solar gain? I know you can get summer bypass but extra cost.. With this system there is also annual maintenance such as replacing and cleaning filters and services every few years.

Demand Control ventilation is pretty much maintenance free but the air being supplied to the house is the same temperature as the outside air. Maybe nice in the summer but not in the winter. Interested in hearing your view calahonda52...

Calahonda52

I suppose the following points sway me towards a properly designed, installed and commissioned MHVR system:

Hugh increase in air quality.
constant airchanges--controlled
constat temperature.
That in itself is enough for me as say you have n 80% efficient rig with a flow rate of 160m3/hr, then roughly it costs 74 euro a year to run, but you are recovering c 300 euro in heat, so even if you spend 100/pa on filters you are still quids in.

The problem I see with DCV is what decides the demand?
there is no air filtering
intuitively is is wrong to be drawing cold air deliberately into the house.:cool:

One way of looking at it is to take the net increase in capital cost between the two and run some payback math based on the expected efficiency

Re the solar gain, if the house is designed properly then that should not be an issue.

On the MHVR, it is key u understand the design
I penned some thoughts in this thread
http://www.boards.ie/vbulletin/showthread.php?t=2057461413
where it seems a top of the range rig was not installed properly.

The design math is neither hard or complex but it needs to be understood by the house owner

BryanF

Calahonda52 wrote: »

but then on south facing, 3 G reduces solar gain during winter

IMO 3G can have adequate solar g factor to still beat 2g in domestic construction.

BryanF

Threebesties wrote: »

As I see it, Mvhr has the added benefit of recovering the heat from the extract air warming up the cooler incoming air. Great in the winter for sure but do you want this in the summer when you have lots of solar gain? I know you can get summer bypass but extra cost.. With this system there is also annual maintenance such as replacing and cleaning filters and services every few years.

Demand Control ventilation is pretty much maintenance free but the air being supplied to the house is the same temperature as the outside air. Maybe nice in the summer but not in the winter. Interested in hearing your view calahonda52...

mvhr for new builds
Dcv for renovations
Run a phpp (passive house calc) and let the numbers do the talking.

Calahonda52

BryanF wrote: »

IMO 3G can have adequate solar g factor to still beat 2g in domestic construction.

I agree.
I am old school and as such I have an aversion to relying on the various claims made re stuff u can't see such as low this and high that etc etc, especially for glass.
I have had 3G windows removed because with the glass was the wrong way around or inside out etc.
We don't call it KISS for nothing

npgallag

We are going for a HRV system and an air to water heat pump with UFH. Full system supplied and installed by a midlands renewalbles company

Calahonda52

npgallag wrote: »

We are going for a HRV system and an air to water heat pump with UFH. Full system supplied and installed by a midlands renewalbles company

What does the HRV system look like
Not the make of the rig but
Specific fan power
flow rates in the rig intake and exhaust, as well as duct sizes
position and number of silencers
air velocities at the extract and supply diffusers
duct diameters and type to room extract and supply
Treated floor area of house.
Where the unit will be fitted and how accessible is it to change the filter.
Does it have a boost option at local level rather than just centrally at the unit?

npgallag

Dimplex 8Kw air source heat pump..air flow 3100 m3/h
unit fitted outside garage.
AHVS Kenetic plus
Main trunk 150mm ducting, branch line 120mm.
House Floor area 210m/sq

Calahonda52

AHVS Kenetic plus: can't find it:(

air flow 3100 m3/h for the HP, I was asking about the MHVR

npgallag

http://www.vent-axia.com/product/sentinel-kinetic-plus-b.html

Calahonda52

npgallag wrote: »

http://www.vent-axia.com/product/sentinel-kinetic-plus-b.html

Nice rig, you might find this interesting:
http://www.cmhc-schl.gc.ca/odpub/pdf/62043.pdf