Pulling the final trigger... to selfbuild or not to selfbuild..

[puntloos]

6 hours ago, Adsibob said:

There's a good amount of detail here, but you could add more. For example, you specify the thickness of PIR in the buildups, but I'm not sure all PIR is equal. Aren't there different types?

 

I'm sure there's more than one brand/type but it feels the details are mostly academic

 

6 hours ago, Adsibob said:

Similarly, in one part you state "100mm of sound insulation", but that is area where there are all sorts of densities and materials available. You should choose something specific and specify it.

True, should spec.

 

6 hours ago, Adsibob said:

 

Your skylights don't show any insulation detail. Velux for example supply insulation collars for their skylights separately. Similarly, flashing kits don't appear to have been specified. These are all things I assumed would be included as part of my tender and then discovered they weren't. Added cost and the surprise is never welcome.

A couple of other amendments you should consider:

• If the loft is intended to be usable space, rather than just storage, I would seriously consider investing in:
  • wood fibre insulation. You need quite a lot of thickness to make it worthwhile, at least 160mm but preferably more, and of course you'll need to run calcs to make sure your build up complies with regs, which bizarrely only care about insulation in winter, not summer. This will increase the decrement delay making it cooler by delaying the heat transfer time to a time when it is cooler outside so that you can open the windows and purge heat quickly; and

Certainly planned to be extendable to living space, I'm somewhat surprised that it's not good by default in your view? The roof has 150mm PIR in there already? Or where would you insulate?

6 hours ago, Adsibob said:

• • external blinds for your two skylights.

Yeah, the skylights need to be blinded, I suppose I implicitly assumed, good to call out

6 hours ago, Adsibob said:

• For sound proofing, where you've specified 15mm of soundbloc plasterboard. It's better to double up on this and stagger the joints.

Not sure I follow, do you have perhaps a drawing/URL with some info on this? Of course double is better 😃 - but not sure where the extra space would go..

6 hours ago, Adsibob said:

• Have you specified the pipe thickness and type for the UFH? I couldn't see that.

No, that's again left up as an exercise for the reader (a.k.a. something the builder can skimp on. Thanks )

[Adsibob]

2 hours ago, puntloos said:

The roof has 150mm PIR in there already?

PIR is awful for summer. building Regulation compliance will only keep you comfortable  in winter and sweaty in summer. If you want to use that space, make it comfortable by designing for all seasons.

[Adsibob]

2 hours ago, puntloos said:

No, that's again left up as an exercise for the reader (a.k.a. something the builder can skimp on. Thanks )

I would not leave pipe diameter and spacing to your builder. Makes a massive difference to output and performance, as well as ability to change heating source in future.

[Adsibob]

2 hours ago, puntloos said:

Not sure I follow, do you have perhaps a drawing/URL with some info on this? Of course double is better 😃 - but not sure where the extra space would go..

What I meant by this was that with one layer, there is actually nothing to prevent the sound going through the gaps along the joints of the plasterboard. If you reduce your ceiling height by 15mm, you can install an additional layer of plasterboards and stagger them so that the joints of the first layer are covered by the second layer. It’s double the materials, and more work obviously, though not double as you are still only plastering once, you are just boarding twice. But you will get a much better result.

[Gus Potter]

On 31/07/2022 at 08:14, MikeSharp01 said:

Probably more if you go the full architect route but if you have vision and are ready for hard, often relentless, work you will make it to the end. You will have A. The satisfaction of having done it. B. Much better equipped in all kinds of situations you will find yourself in the future - because you understand the challenges of constructing a home, you have grown in confidence with a wide range of skills and, C. There will be this artefact on the street that will be testament to your work for generations yet to come who will, if you build it to be light on the planet, thank you for it.

Like your train of thought Mike.

 

Having reflected on this over the years and reading the posts on BH I'm minded to conclude that professional / sage advice can help a lot if sought and given at the right time.

 

Having been through the self build journey myself, then been a contractor building other folks houses and now a designer on reflection I would encourage all those starting out to get a bit forward under their own steam then spend the 300 - 500 quid finding someone who will tell them what they need to learn next and where the big pitfalls lie. I would not have done this at the time but on reflection life would have been much easier if I had done just that!

 

But the reality is that the younger generations always think they have invented a new wheel.. the older generations just need to suck it up..and let the younger folk get old and learn the hard way. But unless they learn the hard lessons in life they will never grow up.. and we need the younger generation to grow up so they can pay our pensions!

 

 

 

 

 

[puntloos]

21 minutes ago, Gus Potter said:

Like your train of thought Mike.

 

Having reflected on this over the years and reading the posts on BH I'm minded to conclude that professional / sage advice can help a lot if sought and given at the right time.

 

Having been through the self build journey myself, then been a contractor building other folks houses and now a designer on reflection I would encourage all those starting out to get a bit forward under their own steam then spend the 300 - 500 quid finding someone who will tell them what they need to learn next and where the big pitfalls lie. I would not have done this at the time but on reflection life would have been much easier if I had done just that!

 

But the reality is that the younger generations always think they have invented a new wheel.. the older generations just need to suck it up..and let the younger folk get old and learn the hard way. But unless they learn the hard lessons in life they will never grow up.. and we need the younger generation to grow up so they can pay our pensions!

 

No no you're all wrong and I am too genius to take advice!

 

OK OK seriously, as with many things in life I struggle a lot with 'the things I don't know that I don't know'. For example I had to find out at some point that I needed more detailed SE drawings, and for that I needed soil samples taken and for that I needed to .. etc.

 

It's all not "rocket science" but finding this out step by step costs a _huge_ amount of time, which was just the thing I tried to avoid... (fail). But like you said @Gus PotterI actually did pay people for their advice. I've paid 3-5-900 quid one-off consultancy fees to the likes of builders to look over my (then-)current plans, architects and project managers to tell me what stuff I needed to take care of urgently, M&E team to design a good heating system. And at the same time all of them predicting I could start building in 3-max-4 months from now for sure.. (that was early 2021..)

 

And even after this paid-for advice I had those advisors forget to mention things like soil samples, soakaway testing. I might've paid the wrong people, who knows. Not that they were dumb or inept, they might just have were creators, not teachers, or who knows maybe I didn't listen properly, I'm sure I made many mistakes (made wrong assumptions) myself too.

 

And I'm not even sure, after these 3 years of house design, if i could comfortably advise the next person who walks into the door. But at least Ive had a good amount of extra eyes, esp thanks to buildhub, to look at the things I've been doing. And ha, even this late in the game @Adsibob is suggesting a few items I certainly need to take another look at. 

 

I'm fairly sure my basic design is solid and buildable, and I have good confidence I found a decent team that's not over-charging.. (one tender just came back at nearly double the quote of my first choice). Phew, and the ride is just starting.

 

 

Edited August 2, 2022 by puntloos

[Gus Potter]

9 minutes ago, puntloos said:

No no you're all wrong and I am too genius to take advice!

Sorry if any offense caused . Did not wish to come over as patronising but have , wrong choice of words from me, on reflection would have used different language.

 

15 minutes ago, puntloos said:

And I'm not even sure, after these 3 years of house design, if i could comfortably advise the next person who walks into the door.

Bet you could, it's not just the building theory you learn it's all that tacit knowledge you've gained on the way that you can't put a price / value on.

 

All the best.

 

Gus

[puntloos]

2 minutes ago, Gus Potter said:

Sorry if any offense caused . Did not wish to come over as patronising but have , wrong choice of words from me, on reflection would have used different language.

 

You know I was joking, right? Just checking - you've been very insightful and Id be silly to ignore experienced builders here, in fact that's why I'm hanging around in the first place.

2 minutes ago, Gus Potter said:

Bet you could, it's not just the building theory you learn it's all that tacit knowledge you've gained on the way that you can't put a price / value on.

 

All the best.

 

Gus

Indeed, will be around..

[Jilly]

You will understand much more when you actually do it. And there are 100's of things you don't know cos you don't know, sometimes until there's a stuff up and you think that doesn't look right... so you research and find out the 100 ways to skin the cat and then wish you'd done something different way back, but it's too late... You have to let some things go in the end, and remind yourself you only care because its your baby, a developer would hide/fudge/compromise/not have worried in the first place and carry on. 

[puntloos]

On 01/08/2022 at 20:33, Adsibob said:

PIR is awful for summer. building Regulation compliance will only keep you comfortable  in winter and sweaty in summer. If you want to use that space, make it comfortable by designing for all seasons.

hmm, your point about decrement delay is interesting. You are assuming "purging heat" (which by the way is certainly a design element of my house, we have designed effectively a whole-house chimney stack hallway) but I always thought passivhaus was assumed to be airtight all year round? Or is this just more realistic?

 

And you're saying PIR is not great for loft but do you think it's fine everywhere else? Or would you do wood fibre everywhere?

[puntloos]

On 01/08/2022 at 20:34, Adsibob said:

I would not leave pipe diameter and spacing to your builder. Makes a massive difference to output and performance, as well as ability to change heating source in future.

Do you know a good default for diameter and spacing? What would you recommend?

[puntloos]

On 01/08/2022 at 20:46, Adsibob said:

What I meant by this was that with one layer, there is actually nothing to prevent the sound going through the gaps along the joints of the plasterboard. If you reduce your ceiling height by 15mm, you can install an additional layer of plasterboards and stagger them so that the joints of the first layer are covered by the second layer. It’s double the materials, and more work obviously, though not double as you are still only plastering once, you are just boarding twice. But you will get a much better result.

I can live with 15mm less. Good idea, thank you.

[Adsibob]

13 minutes ago, puntloos said:

hmm, your point about decrement delay is interesting. You are assuming "purging heat" (which by the way is certainly a design element of my house, we have designed effectively a whole-house chimney stack hallway) but I always thought passivhaus was assumed to be airtight all year round? Or is this just more realistic?

 

And you're saying PIR is not great for loft but do you think it's fine everywhere else? Or would you do wood fibre everywhere?

It's quite complicated to figure out what is the ideal combination for any given situation. It will depend on various parameters and you will need to run the calcs to make sure you meet your BCO's requirements.

Just by of example, this is what I did, but the outcome was not as good as i wanted. An extra 40mm or so of wood fibre would have helped I think:

[puntloos]

Well.. we're going for it. Of course still a few steps like signing contract but we've called everybody and.. it's off to the races.

 

I'm ... debating.. if I should write a blog on this or not.. 

 

 

 

[Mr Punter]

On 01/08/2022 at 20:33, Adsibob said:

PIR is awful for summer. building Regulation compliance will only keep you comfortable  in winter and sweaty in summer.

 

Do you have a link that substantiates your assertion?  It sounds like nonsense, possibly based on the hot summer and your house maybe gets a bit of solar gain and has no a/c.

[Pocster]

40 minutes ago, puntloos said:

Well.. we're going for it. Of course still a few steps like signing contract but we've called everybody and.. it's off to the races.

 

I'm ... debating.. if I should write a blog on this or not.. 

 

 

 

Good for you ! Enjoy the ride / car crash / cost 😁👍

[Pocster]

On 02/08/2022 at 08:38, Jilly said:

You will understand much more when you actually do it. And there are 100's of things you don't know cos you don't know, sometimes until there's a stuff up and you think that doesn't look right... so you research and find out the 100 ways to skin the cat and then wish you'd done something different way back, but it's too late... You have to let some things go in the end, and remind yourself you only care because its your baby, a developer would hide/fudge/compromise/not have worried in the first place and carry on. 

Crumbs @Jilly - you sure I didn’t PM you that paragraph. You are of course right . How can you know something you don’t know . The answer is you do it and f it up ! . Now you know ! 

[Kelvin]

Well done.  
 

I’ve been through the mill with this too. Some days I get a bit down about even starting this. We could have bought a wee cottage with a little bit of land and invested the rest. We’ve been at it a year almost to the day from putting an offer in on the land until now a few weeks away from a full planning decision ( we have PIP) Even just trying to get people to quote has been a trial. Everything takes much longer than I was expecting. Naively I thought we’d be started by now. The constant news cycle of everything going up in price takes us from having a comfortable budget to it might actually be a bit tight. Not at all where I wanted us to be. However, it just means compromising on certain things. I was willing to spend a big sum on wholehome automation but have removed that from the list. The garage was going to be a mini version of the house now it will be a steel building etc 
 

However, that’s some days. Other days I feel excited about it all and want to get going. We are committed to do it now both emotionally and financially so what will be will be. 

Edited August 12, 2022 by Kelvin

[Kelvin]

Oh I definitely keep a blog even if it’s for yourself. You make so many decisions along the way that you’ll both forget you made it and then when you remember you’ll forget why. Take 100s of pictures and video too. Well that’s my plan anyway. 😂 

[Marvin]

And don't forget to engage the EPC inspector BEFORE you cover up the building insulation to avoid drilling holes in walls later.....🙄

[puntloos]

46 minutes ago, Kelvin said:

Well done.  
 

I’ve been through the mill with this too. Some days I get a bit down about even starting this. We could have bought a wee cottage with a little bit of land and invested the rest. We’ve been at it a year almost to the day from putting an offer in on the land until now a few weeks away from a full planning decision ( we have PIP) Even just trying to get people to quote has been a trial. Everything takes much longer than I was expecting. Naively I thought we’d be started by now. The constant news cycle of everything going up in price takes us from having a comfortable budget to it might actually be a bit tight. Not at all where I wanted us to be. However, it just means compromising on certain things. I was willing to spend a big sum on wholehome automation but have removed that from the list. The garage was going to be a mini version of the house now it will be a steel building etc 
 

However, that’s some days. Other days I feel excited about it all and want to get going. We are committed to do it now both emotionally and financially so what will be will be. 

 

Ha, May 2019 is when we bought the 'poor state house, nice plot'. At the time I expected to have the big metal ball hit the house in early 2020. But then someone ate a bat. <sigh> 

 

Not that covid was the only thing causing delays. The shocking thing to me was that I've had a bunch of experts that all basically were horriblyhorribly wrong about when we could "really start". Certainly I was also a weak/slow link by having major design influence etc. But so.. many.. things 

 

I might create a sooper brief blog but yeah. I still think it is the right choice. But yeah let's keep it up, my brother-from-another-..builder? or something.

 

[Adsibob]

1 hour ago, Mr Punter said:

 

Do you have a link that substantiates your assertion?  It sounds like nonsense, possibly based on the hot summer and your house maybe gets a bit of solar gain and has no a/c.

Yes i think so, this site says: "insulation materials offering a high decrement ‘factor’ include cellulose fibre (7.3 hr), wood fibre insulation board (11.3 hr); whereas materials with a low decrement factor would include low-density mineral fibre (3.7 hr) and polyurethane/polystyrene." I appreciate polyisocyanurate is not exactly the same as polyurethane/polystyrene, but they are similar enough for present purposes.

 

This site gives technical specs of wood fibre and of PIR as follows:

 

Wood fibre

 

Thermal conductivity/ λ (lambda)  W / m . K = 0.038

Thermal resistance at 100mm K⋅m²/W = 2.5

Specific Heat Capacity J / (kg . K)= 2100

Density kg / m³ = 160

Thermal diffusivity m²/s  = n/a

Embodied energy MJ/kg = n/a

 

PIR

Thermal conductivity/ λ (lambda)  W / m . K = 0.023–0.026⁽¹⁸⁾

Thermal resistance at 100mm K⋅m2/W = 4.50

Specific Heat Capacity J / (kg . K) = n/a

Density kg / m3 =  30 – 40

Thermal diffusivity m²/s  = n/a

Embodied energy MJ/kg = 101 ⁽¹⁷⁾

Vapour permeable: No

 

That site also has a page which states the following:

 

Thermal Diffusivity

Thermal Diffusivity ties the above factors together into an equation that measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy.  In effect it is a measure of thermal inertia or ‘buffering’.

The equation is:

Thermal diffusivity = thermal conductivity / specific heat capacity x density

Examples:

• Rigid polyurethane insulation has a thermal diffusivity of approximately 4.46 x 10-7 m2/s
• Timber fibre insulation has a thermal diffusivity of approximately 1.07 x 10-7 m2/s
• Copper has a thermal diffusivity of around 1.11 × 10−4 m2/s

In a material with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'.

In the above three examples we can see that heat races through copper while it moves more rapidly through rigid polyurethane than it does through timber fibre board." (my emphasis)

 

Again, I appreciate polyisocyanurate is not exactly the same as polyurethane, but similar enough.

 

To do the proper comparison, one would need to do the decrement delay cals. We did them and found that PIR wasn't as good as wood fibre.

 

If you're still in doubt, see this site, which says:

 

"For a given U value, wood fibre has almost twice the decrement layer of mineral wool and at least 65 per cent more than PIR.  So essentially if you have two walls that have the same U value, it will take twice as long for the heat to get a wood fibre wall as it will through a wall using mineral wool.  How that translates to a building is that during the summer you end up with a building that essentially doesn’t overheat.  It maintains its internal temperature and stays very stable internally.

In volume for volume, flexible wood fibre stores about 12 times more heat than fibreglass and rigid wood fibre boards store about 12 times more heat than PIR, and around 15 times more heat than EPS. So again, on every metric the wood fibre is outperforming the synthetic materials.  This creates buildings that are very stable in the summer.  You’re reducing your overheating risk, so you’re making the building much safer for occupants.  Also that heat absorption lowers heat demand.  It can absorb heat during the day and slowly release it during the evening, so again it’s keeping the internal environment much more stable.  It’s ability to manage moisture also preserves timber, so wood fibre is able to buffer humidity in walls and even out humidity so that you don’t get accumulations in existing timber.  It prevents mould growth and it enables safe refurbishment of building."

 

Note that the insulation in my roof has a significant amount of wood fibre, as well as some PIR. My issues though are that I've not yet blocked out the solar gain coming in through glazing - on the to do list.

 

Edited August 12, 2022 by Adsibob

[puntloos]

1 hour ago, Adsibob said:

Note that the insulation in my roof has a significant amount of wood fibre, as well as some PIR. My issues though are that I've not yet blocked out the solar gain coming in through glazing - on the to do list.

 

Great amount of detail, but can I ask a quick dumb question, which is: "is there any reason ever to use PIR then?" Under what circumstances?

[Roger440]

21 minutes ago, puntloos said:

Great amount of detail, but can I ask a quick dumb question, which is: "is there any reason ever to use PIR then?" Under what circumstances?

 

Cost? V woodfibre that is.

[Adsibob]

17 minutes ago, puntloos said:

Great amount of detail, but can I ask a quick dumb question, which is: "is there any reason ever to use PIR then?" Under what circumstances?

PIR certainly has its uses. It is cheaper than wood fibre, and will achieve better u values for a given budget and a given depth of build up. The only real compromise is on decrement delay, and sustainability. If I had more space available, I probably would have swapped out my thin layer of PIR backed plasterboard for more wood fibre products, and passed the U value required by our BCO  with no PIR insulation at all. But alas we weren’t properly building from scratch, we were renovating an existing 1930s semi and we didn’t have an unlimited budget.