Help please balancing specification with budget

[JohnW]

I’m in a real quandary and I’m hoping you guys can help me decide on the way forward…

I’m building in Northern Ireland (currently at the detailed drawings stage) and had my mind set on achieving the following specification (U-values in brackets)…

·         Floors

o   Ground (0.14 W/m²K)

§  UFH in 100mm screed

§  125mm foil backed polyurethane

§  sub-floor

o   First

§  UFH in 75mm screed

§  50mm insulation

§  hollow-core slab

§  150mm void for services (including MVHR ducting)

·         Walls

o   External (0.15 W/m²K)

§  Sand/cement plaster

§  100mm block

§  200mm cavity fully filled with pumped in grey beads & glue

§  100mm block

§  Sand/cement plaster

·         Roof

o   Warm roof (0. 13 W/m²K)

§  100mm insulation on top of rafters

§  125mm Spray foam insulation between rafters

§  Plaster board with foil backing

·         Glazing

o   Triple glazed Windows (0.85 W/m²K glass & frame combined)

·         Heat source (no mains gas available)

o   Domestic hot water – Air Source Heat pump (using Economy 7 at night)

o   Heating – Air Source Heat pump (using Economy 7 at night)

·         Mechanical Ventilation with Heat Recovery

·         Air tightness target 1m³/hr/m²

HOWEVER… now that I’ve started getting prices, it’s obvious that this approach is exceeding my budget.

I don't want to reduce the size of the house, so I believe I have 2 options;

1.       Find a cheaper way of achieving the same target values or

2.       Reduce the spec and settle for "lower" target values

I appreciate that this is a very generalised question but, I welcome any advice from forum members as to which of the 2 options they would recommend and also some detail on how to achieve the recommended approach.

 Thanks

John

[PeterW]

Consider this ..

 

Floors (still achieving u Value)

o   Ground (0.14 W/m²K)

§  UFH in 100mm screed structural slab

§  125mm foil backed polyurethane

§  sub-floor

o   First

§  UFH in 75mm screed  22mm Weyroc/Egger Chipboard

§  50mm insulation  75mm fibre (soundproofing)

§  hollow-core slab  Metal Web Joists

§  150mm void for services (including MVHR ducting)

·         Walls

o   External (0.15 W/m²K)

§  Sand/cement plaster

§  100mm block

§  200mm cavity fully filled with pumped in grey beads & glue

§  100mm block

§  Sand/cement plaster

·         Roof

o   Warm roof (0. 13 W/m²K) (assuming 195mm rafters)

§  100mm insulation on top of rafters   40mm PUR below rafters

§  125mm Spray foam insulation between rafters   195mm Frametherm 35

§  Plaster board with foil backing 

 

 

Not sure why you need UFH first floor..? The floor build up using web joists will allow your service void to be eliminated. It also probably reduces your floor depth and associated costs of additional walls. Structural slab may also help with depth of dig out and costs there too.

 

What size is the proposed property..?

[JohnW]

21 minutes ago, PeterW said:

Not sure why you need UFH first floor..? The floor build up using web joists will allow your service void to be eliminated. It also probably reduces your floor depth and associated costs of additional walls. Structural slab may also help with depth of dig out and costs there too.

 

What size is the proposed property..?

Thanks @PeterW, I'm not sure about the UFH upstairs either to be honest, but it's what our energy consultant recommended. Considering the good U-Values in the floor, walls & roof what heating would you suggest for upstairs?

 

The property will be approx. 200m².

 

[AliG]

A lot depends on what the key points of your specification are and what kind of house you want.

 

In general though losing 0.01/2 points from U-values often reduces the cost massively whilst making little material difference to heating costs so I wouldn't get too hung up on specifics for each item and would think more about the insulation levels of the whole house.

 

I have hollowcore upstairs floors as they are more solid, but as @PeterW points out the are considerably more expensive. Not only are they more expensive, but due to the need to leave room for services you need to build a taller house and/or dig more down into the ground which adds to costs. So it depends on how determined you are to have a concrete first floor.

 

PIR insulation is very expensive, I was horrified at some of the costs. The easiest saving is probably using thicker mineral wool type insulation in the roof rather than PIR, it will be less than half the cost. Again though this will depend somewhat on your roof design, whether or not you want to use the space under it etc. As far as I could figure out spray foam insulation offers no better U-value than mineral wool at the same thickness yet is much more expensive.

 

220mm rafters with 220mm Knauf Omnifit Stud (0.034 W/mK) would give you a similar U-value roof for way less. It would also be thinner. If you want a better U-value you can add insulated plasterboard underneath.

 

A raft foundation on EPS with UFH in the concrete raft should be cheaper. Alternatively, you can save money by simply making the screed thinner. You only need 60mm of liquid screed for UFH, indeed it will work faster in thinner screed.

 

If the insulation's good enough you can eliminate the upstairs UFH and the insulation and just use 30mm screed to smooth off the hollowcore if you want to stick with hollowcore. You can always put in pipework for radiators just in case upstairs.

 

Make sure that the floor insulation isn't quoted as special UFH insulation which is way more expensive and a con. Standard PIR is fine under UFH.

 

 

 

Edited May 3, 2017 by AliG

[Ferdinand]

Just now, JohnW said:

Thanks @PeterW, I'm not sure about the UFH upstairs either to be honest, but it's what our energy consultant recommended. Considering the good U-Values in the floor, walls & roof what heating would you suggest for upstairs?

 

The property will be approx. 200m².

 

 

Pretty much none. Or possibly a couple of electric radiators for use a few weeks a year.

 

(Other people on here will give you more precise answers specifically related to u values etc.

[ragg987]

Might be worth reviewing the method as well.

 

foundations - trenched foundation or piling vs floating slab (as PeterW, I think)

external walls - timber frame

screed - apart from PeterW's suggestion, how about liquid screed - you can get away with 40mm depth, less materials and less drying time

 

One factor to bear in mind is price variations - e.g. the moment you need to dig into the ground out you will risk issues and hence price escalation. If your methods mean you are more "assembling" on site rather than making on site you can reduce the variability.

 

Our house has u-values of approx 0.11 for wall, roof and floor. We still needed heat on first floor and are unable to rely on the heat from ground floor rising up (UFH), we use a direct electrical heater through the MVHR to top it up on really cold days.

[JohnW]

Thanks @Ferdinand, I've asked some specific questions regarding upstairs UFH in the relevant sections and I appreciate that if the spec is good enough we may not need heating upstairs, however I'm more concerned with how I can reduce the cost of achieving that high spec or alternatively how I can reduce the high spec to acceptable levels.

[JohnW]

4 minutes ago, ragg987 said:

Might be worth reviewing the method as well.

 

foundations - trenched foundation or piling vs floating slab (as PeterW, I think)

external walls - timber frame

screed - apart from PeterW's suggestion, how about liquid screed - you can get away with 40mm depth, less materials and less drying time

 

One factor to bear in mind is price variations - e.g. the moment you need to dig into the ground out you will risk issues and hence price escalation. If your methods mean you are more "assembling" on site rather than making on site you can reduce the variability.

 

Our house has u-values of approx 0.11 for wall, roof and floor. We still needed heat on first floor and are unable to rely on the heat from ground floor rising up (UFH), we use a direct electrical heater through the MVHR to top it up on really cold days.

Thanks @ragg987, interesting to hear that you have very low u-values but still need heat on the upper floor.

 

We are considering liquid screed for the ground floor and also UFH in slab as per @PeterWs suggestion.

 

It seems that achieving very good airtightness is expensive along with the expense of the required MVHR system. We frequently have windows open in our current house which has poor insulation & airtightness.

[Ferdinand]

1 hour ago, JohnW said:

1.       Find a cheaper way of achieving the same target values or

2.       Reduce the spec and settle for "lower" target values

 

3 Buy well.

 

There are quite a few threads on how to reduce costs, including this one about buying well, with dozens of suggestions of how to shave 5-10% off the *payment* side.

But my top tip would be to know what you will definitely need, then get a dry, secure storage facility (eg container or double garage), and buy things in advance when you see them reduced. That way you will be able to get a lot of your basics for 40-60% of their retail price. To buy months in advance I would want at least 30-40% off, which is achievable for many items.

 

eg I have just bought a pallet of 50mm celotex at £10 per 8x4 sheet delivered (Wickes - about £25). Someone here pointed out foil faced 125mm celotex at £25 a sheet a couple of weeks ago (normally £40-50 even at cheap online orders). Ditto I just bought 25 sheets of OSB3 at £13 per sheet delivered - OK but others will have done better on that. Equally I am currently looking at doors, and it is possible to source Oak Veneered heavy doors with posh door furniture for approx £80 each, which is the cost of a mid-range pine at a DIY shed.

 

If you do that with as much as possible, and are not too persnickety about *precisely* what you want, that could save 10s of k.

 

I'll leave the ufh for the other thread then; the point is to design things out you  do not need exactly by going for a high spec.

 

Ferdinand

 

 

Edited May 3, 2017 by Ferdinand

[PeterW]

I'd say your spec isn't a high spec - its a standard build with standard items and has been augmented to get to a better uValue.

 

UFH upstairs is a bit marmite - some say you need it, some say you don't and its a lot to do with airtightness and also the efficiency of MVHR among other things. Replacing sound insulation with thermal insulation between floors to meet part E always causes problems in this scenario.

 

If you want to save on build cost and also get good uValues then you have to think laterally - go for a 140mm blockwork inner skin and then use 200mm EPS board with render as EWI and you have the same uValue with a lower cost to build and thinner foundations. Use 250mm Engineered joists for the roof and you get the option to bury a lot of cheaper insulation into the rafters and get a better uValue. You may also want to review the spec on the floor to go either passive slab or go deeper EPS but it has a converse cost of more muck away.

 

Good airtightness is not expensive, neither is MVHR. You can get a decent unit (assuming we are talking 3/4 bed house) with all the bits for less than £2k. Airtightness takes time and care, but isn't difficult with blockwork if your brickie full fills all the perp ends and points properly. Adding EWI rather than a cavity fill further seals the walls, leaving the ceiling/roof to do which there are plenty of membranes. Its also a DIY job (just ask @ProDave)

 

I've never got this idea of slab and screed, it seems to be an odd way of building up a heated floor.

[AliG]

I have slab and screed. I pushed really hard for a raft foundation but the architect/SE weren't really up for it.

 

One issue may be the weight of a concrete upper floor. My slab is 200mm thick and the supporting walls for the upper floor bear down on it, indeed in some areas I have 2 concrete upper floors, is it is very heavy. I wonder if an SE may have issue with building a heavier structure on a 100mm floating concrete raft. I am sure there are ways around this, but they are very married to their standard methods.

 

To add to what people are saying about buying better, spec changes etc. If you are using a main contractor this is harder to do. What I did though was get an itemised bill then go through all the items to see where the prices seemed oddly high or the spec could be changed to save money. By far the biggest and easiest savings were in making small changes to the spec of the insulation.

 

I would have a good look at what your heating consultant has recommended as I doubt they focused much on cost benefit of various points and this may be driving much of the spec. For example my architect originally specced Kingsapn Kooltherm which has about 10% better insulating properties than PIR but can be much more expensive.

Edited May 3, 2017 by AliG

[Ferdinand]

There is also a lot you can do tactically to stop planners gold-plating their requirements (or getting the gold-plating removed) - but that is quite tactical and situation specific, and by buying and selling (eg digger, security fencing, perhaps scaffolding) rather than hiring.

 

Lots of other aspects too, such as putting a permanent power-cabinet in once rather than having a site supply then the supplier paid again to put one into your house itself. 

 

But that is wandering off topic, so I will juts hint at that and leave it.

Ferdinand

Edited May 3, 2017 by Ferdinand

[Declan52]

Would go with joists either standard or I beam and forget the slab. The extra to do a floor and plus the ceiling underneath will be a big saving.

200mm cavity could be reduced to 175 or 150 will save some money.

Cut roof or attic truss whichever suits better. Take it it's a 2 storey house and not a chalet bungalow. 

Getting the spray insulation is way more expensive than frametherm type. Plus is easily a diy job.

Airtightness in block build ain't that hard. Tape at door window reveals and and wall ceiling junctions. Taping these is a job you can do yourself. I take it you will wet plaster the house inside. 

Bpc have kits for mhrv that aren't expensive(2k) and you can install yourself.

I have ufh downstairs and rads upstairs and it works fine.

As you are in Newcastle the ground will be gd so you can go shallow trench founds.

Realistically how much work can you/ family do???

 

 

[Bitpipe]

UFH upstairs is dependent on how warm you like your bedrooms - our preference is on the cool side so we have no wet UFH upstairs and it was perfectly comfortable last winter - however this is in SE England, would expect NI (where I grew up) to be colder. We have wood floors upstairs so they feel warm underfoot.

 

We did however put electric UFH in the bathrooms under the tile and wet towel rads that are independent controlled.

 

Our house is near passive standard so we can get away with running the GF heating for only a few months of the year, bigger challenge is preventing overheating the rest of the year, even a cool sunny day can have you sweltering if you don't manage the solar gain properly (shading, window position etc).

 

I echo all of the above, many architects and builders work they way they're used to and don't worry too much about saving you money. If you want a good spec on a tighter budget then you need to do research, shop wisely and be prepared to do some jobs yourself where it makes sense (DIY MVHR is a popular one on this forum).

 

 

[jack]

14 minutes ago, Bitpipe said:

UFH upstairs is dependent on how warm you like your bedrooms - our preference is on the cool side so we have no wet UFH upstairs and it was perfectly comfortable last winter - however this is in SE England, would expect NI (where I grew up) to be colder. We have wood floors upstairs so they feel warm underfoot.

 

We did however put electric UFH in the bathrooms under the tile and wet towel rads that are independent controlled.

 

We have a very similar spec house to Bitpipe, but no heating at all upstairs.  Bedrooms are fine without, but we should have gone for heating in the bathrooms, as they get a little more nipply than ideal in winter.  

 

I'm currently planning to install a small IR panel on the ceiling of each upstairs bathroom, which should at least take the chill off the tiles each morning in winter.

[Mr Punter]

@PeterW's best suggestion was to lose the hollowcore on the first floor.  His others were good too.

[jack]

I missed the hollow-core.  Sounds an expensive build-up.

 

If you're adamant about screed upstairs, I'm pretty sure you can liquid-screed even on top of 22mm chipboard + easi-joists if you engineer it right. 

[AliG]

I looked into this. It did seems that you can use screed with post-joists which might be the best of both worlds giving a solid floor and a better material for UFH, but still having a service space between the joists. There may be issues with the weight of the screed and its affects on spans.

[PeterW]

If you really want or need upstairs UFH then look into something such as the aluminium spreader plates under the joists. It is a bit of fun though when it comes to the turns as you can't notch the joists so something such as the thin overfloor system may be needed. 

[Redoctober]

23 minutes ago, AliG said:

I looked into this. It did seems that you can use screed with post-joists which might be the best of both worlds giving a solid floor and a better material for UFH, but still having a service space between the joists. There may be issues with the weight of the screed and its affects on spans.

 

This might assist in understanding what is required for UFH and screed upstairs.

 

PW.

UFH.pdf

[Bitpipe]

36 minutes ago, PeterW said:

If you really want or need upstairs UFH then look into something such as the aluminium spreader plates under the joists. It is a bit of fun though when it comes to the turns as you can't notch the joists so something such as the thin overfloor system may be needed. 

 

We did this on our ground floor, which is suspended timber over the basement. We struggled with the loops that had to span the joist before someone had the bright idea of just bringing them over each joist and securing with a pipe clip, then cutting slots out of the 22mm OSB where the loops ran. Because we were putting another ply layer on this floor before the resin went down, it wasn't an issue.

 

I know HerbJ found a small bore wet system for his first floor that incorporated a soundproof board but it wasn't cheap. He mainly put it in for resell purposes.

 

Forgoing upstairs heat can be a bit of a leap of faith to go without so I had a few plan B's in play. The bathroom towel rads each back onto a bedroom, so a small rad could have been retrofitted back to back if required.

 

It would also be easy to add a switched fused spur to each room for an electric panel heating system, in fact our bathroom UFH was a last minute addition (we'd already started tacking) but it was easy enough to get boxes and conduit in for stats, controllers and the spurs themselves.

 

Really, if your house is well insulated and airtight, then bedroom heat requirements should be minimal.

 

[PeterW]

I plan on spending some money on a decent air tightness membrane and doing that properly to reduce the losses. 

 

I've got one room that I don't have a room below (unheated garage) but that is getting 200mm of well sealed PIR in the floor and all the garage walls are insulated so I'm hoping it will be fine. I may also put an electric panel rad in there or alternatively a heat battery in the MVHR feed. 

[JohnW]

On ‎03‎/‎05‎/‎2017 at 15:00, PeterW said:

If you want to save on build cost and also get good uValues then you have to think laterally - go for a 140mm blockwork inner skin and then use 200mm EPS board with render as EWI and you have the same uValue with a lower cost to build and thinner foundations.

This sounds interesting - have you any more information or links so I could explore this option?

 

On ‎03‎/‎05‎/‎2017 at 15:00, PeterW said:

Good airtightness is not expensive, neither is MVHR. You can get a decent unit (assuming we are talking 3/4 bed house) with all the bits for less than £2k. Airtightness takes time and care, but isn't difficult with blockwork if your brickie full fills all the perp ends and points properly. Adding EWI rather than a cavity fill further seals the walls, leaving the ceiling/roof to do which there are plenty of membranes. Its also a DIY job (just ask @ProDave)

Our architect tells us that we would save approximately £10k if we did away with the MVHR. We are a family that frequently open windows in our current 20 year old house and I can see this continuing in the new house and can see all benefits of MVHR "going out the window". Therefore, if we decide to have no MVHR, I'm wondering is there a minimum airtightness level we should aim for or should we just let the builder build within the regulations i.e. 10m³/hr/m² ? 

 

 

[jamiehamy]

£10k for MHRV?! Are the ducts gold plated?

[JohnW]

On ‎03‎/‎05‎/‎2017 at 15:04, AliG said:

I have slab and screed. I pushed really hard for a raft foundation but the architect/SE weren't really up for it.

 

One issue may be the weight of a concrete upper floor. My slab is 200mm thick and the supporting walls for the upper floor bear down on it, indeed in some areas I have 2 concrete upper floors, is it is very heavy. I wonder if an SE may have issue with building a heavier structure on a 100mm floating concrete raft. I am sure there are ways around this, but they are very married to their standard methods.

 

To add to what people are saying about buying better, spec changes etc. If you are using a main contractor this is harder to do. What I did though was get an itemised bill then go through all the items to see where the prices seemed oddly high or the spec could be changed to save money. By far the biggest and easiest savings were in making small changes to the spec of the insulation.

 

I would have a good look at what your heating consultant has recommended as I doubt they focused much on cost benefit of various points and this may be driving much of the spec. For example my architect originally specced Kingsapn Kooltherm which has about 10% better insulating properties than PIR but can be much more expensive.

Thanks @AliG, I think you hit the nail on the head when you said "...doubt they focused much on cost benefit of various points...", that is exactly what I'm trying to determine.

 

In general I completely understand the benefits of low u-values & good airtightness, but at what cost, and how long it will take to recoup that cost based on the ongoing savings, i.e. return on investment? I'm trying to find that elusive balancing point.

 

I will be using a main contractor and know that I will be limited in my options, but when it comes time to trim the price, I want to discard the right items.