Owner-Builder looking to build our family home!

[AccidentalSkydiver]

Hi All,
 I'm Jack! A chartered engineer from the Midlands who's looking to build our family home - Many moons ago did a carpentry/joinery apprentice Level 3 working on and off build sites, stair cases, extensions, hand cut roof trusses, orangeries etc etc then went on to Uni to study a MEng in Mechanical and Software engineering 📐🛠️ 

I've spent my last 6-8 months meticulously planning, drawing, obsessing, reading, watching, modelling etc and recently discovered the forum so thought I'd come and join to say hello... especially as this seems a more likely source of content and information for my circumstance in the UK than many many sites that are US oriented!

Plan is to build a 'typical' North American stick frame construction internally, but with a masonry skin on the outside. Running with External and Internal load-bearing walls in 2x6 (45x150mm nominal) 600mm OC to allow for more insulation, but then some non-load bearing partitions (utility / downstairs WC and the walk in wardrobe in master bed) in 2x4 at 400mm OC where they don't need that heavy gauge construction. 

looking to have a thermally efficient and stable home, looking to be net-zero energy by utilising stuff like solar and natural heating from the get go.

Looking to sticking around and the journey!

Thanks,
Jack!
 

[markc]

Welcome, sounds like you have been doing your homework

[AccidentalSkydiver]

57 minutes ago, markc said:

Welcome, sounds like you have been doing your homework

Thanks! It's all I've been doing! I'm a bit obsessed 😁 My mrs is sick of me talking about it now. 

Edited March 11, 2022 by AccidentalSkydiver

[joe90]

13 minutes ago, AccidentalSkydiver said:

My mrs is sick of me talking about it now. 

Welcome, they all think that but will (should) be pleased with a well designed/built house 🤷‍♂️, I considered stick build, have a look at “Larsen truss”, less wood and more room for insulation. We welcome all the questions, including stupid ones (we have all been there) and stupid is not asking. A wealth of knowledge here in many different build types.

 

p.s. How can you be an “accidental skydiver”? We’re you pushed? (I am an ex sky diver) 🤣

[ProDave]

Hi and welcome.

 

My view, 6*2 frame is not wide enough to get enough insulation.  We built with an 8 * 2 frame on the outside and then a further 100mm of external insulation around the outside of the frame.  Remember an outer blockwork skin is just a rain shield, it adds very little to the insulation.

[AccidentalSkydiver]

11 minutes ago, joe90 said:

Welcome, they all think that but will (should) be pleased with a well designed/built house 🤷‍♂️, I considered stick build, have a look at “Larsen truss”, less wood and more room for insulation. We welcome all the questions, including stupid ones (we have all been there) and stupid is not asking. A wealth of knowledge here in many different build types.

 

p.s. How can you be an “accidental skydiver”? We’re you pushed? (I am an ex sky diver) 🤣

 The name is because I fell off a cliff when doing UOTC, shattered my shin, smashed my knee to bits. Left leg was pointed <- way, the CO said something to the nature of "You were going for para, guess you're now an accidental skydiver" as I was being packed up for medevac. 

Those trusses look interesting 🤔 will have to investigate just wondering about costs - doing majority of the work myself is going to alleviate some budget restraints, I'd planned out a costing sheet based on some calculated verticals on a sketchup model, with about 25% added for additional structural components

[joe90]

17 minutes ago, AccidentalSkydiver said:

will have to investigate just wondering about costs

You can make your own using scraps of OSB 👍

18 minutes ago, AccidentalSkydiver said:

The name is because I fell off a cliff

Oh shit.

[AccidentalSkydiver]

27 minutes ago, ProDave said:

Hi and welcome.

 

My view, 6*2 frame is not wide enough to get enough insulation.  We built with an 8 * 2 frame on the outside and then a further 100mm of external insulation around the outside of the frame.  Remember an outer blockwork skin is just a rain shield, it adds very little to the insulation.

Hello,
 So calculated (on a less than accurate, I'm sure) on a couple of sites, which 'calculates' that the overall efficiency would be around 0.0266U / R37.5, Others somewhere in the 0.034U / R29 - far past what we require in the midlands, mileage may vary I suppose- I know it gets cold up in the highlands   Here's a diagram of my layout, however, It should be noted I'm considering swapping round the PIR Foam / OSB3 layers and using a SIGA seam tape and replacing the PIR foam with another rigid foam like Polyisocyanurate or something, but lots of this is still up for debate and research!

Also, not shown here because I can't model that small, vapour barriers!

Edited March 11, 2022 by AccidentalSkydiver

[joe90]

1 hour ago, AccidentalSkydiver said:

0.034U / R29 - far past what we require in the midlands,

The mantra on this site is insulation, insulation, insulation, especially with the energy crisis looming. Some here have virtually no heating because their insulation is so good, and you only buy insulation once. My heating comes on a few times fir a couple of months only.

[Simplysimon]

+1 to @ProDave suggestion, we used 350mm I beams for walls, roof and floors with blown cellulose, u value if 0.11

[SteamyTea]

Welcome.

Insulation should not be look at in isolation.

As you fancy being net zero, you have to look at your self generation capacity. PV probably. This, to a certain extent, sets your roof type and size. 

Quite simply, the less energy you need, the less you have to generate. So just thinking that there is not much difference between say a U-Value of 0.12 and 0.1 rather misses the point. It is the temperature distribution that becomes important, this may be skewed to more cold days than warm days. It is because of that you start paying the price.

 

What are you doing for water and waste?

 

 

 

 

 

[TerryE]

16 hours ago, joe90 said:

The mantra on this site is insulation, insulation, insulation,

Have a read through my blog @Jeremy Harris and others.  You have Slab losses, wall losses, fenestration losses, roof losses, air exchange losses, and thermal bridging losses.  You need to design a house with a sensible balance to optimise so that you get a delta £s invested on any one that gives the best drop in heat losses and therefore delta £s in running costs.  As with my and Jeremy's calcs, you don't need anything too sophisticated like the PHPP model which as so many terms and adjustments that it is intractable to make trade offs. 

 

With TF, as Dave says 8×2 + an extra layer of slab insulation can get a U-value of 0.12; slab and roof same ballpark; decent triple glazing under 1.0.  Once you are in this domain 40+% of your heat losses are from air exchange if you have a pretty airtight house and MVHR; up to 85% if you use poor quality conventional build techniques and no MVHR, so you need to make your house airtight by design.  The MVHR means that it always smells fresh because you are continually replenishing with (reheated) external air.

 

If doesn't matter how good the nominal design is if your builder doesn't bother putting in the roof or wall insulation where you can't see -- as many have discovered with a FLIR camera once they've moved in.  Ditto thermal bridges on steel I-beam crossing the warm / cold divide.

 

The single biggest cost component in our house was the natural local stone skin -- which was a planning requirement, as well as looking nice.  As to the near-passive performance, adding this was maybe 15% of the cost of the skin, but then again I use a 3kW inline heater to heat my water-based UFH system and our internal temp is ~ 22½°C everywhere, all year round.  Putting the water-base UFH loops in the slab cost ~$2K  and no other CH installation, rads on walls etc needed.  (The 22½°C is because a pair of OAPs like it that way.)

Edited March 12, 2022 by TerryE

[Iceverge]

Welcome welcome. 

 

Spend £150 ish and buy a copy of PHPP.

 

With an engineering brain it's actually quite possible you'll enjoy it. Looking at the numbers (which are all just school level physics) brings amazing clarity to design in an industry that is rife with misconceptions. 

 

[AccidentalSkydiver]

On 12/03/2022 at 10:05, TerryE said:

Have a read through my blog @Jeremy Harris and others.  You have Slab losses, wall losses, fenestration losses, roof losses, air exchange losses, and thermal bridging losses.  You need to design a house with a sensible balance to optimise so that you get a delta £s invested on any one that gives the best drop in heat losses and therefore delta £s in running costs.  As with my and Jeremy's calcs, you don't need anything too sophisticated like the PHPP model which as so many terms and adjustments that it is intractable to make trade offs. 

 

With TF, as Dave says 8×2 + an extra layer of slab insulation can get a U-value of 0.12; slab and roof same ballpark; decent triple glazing under 1.0.  Once you are in this domain 40+% of your heat losses are from air exchange if you have a pretty airtight house and MVHR; up to 85% if you use poor quality conventional build techniques and no MVHR, so you need to make your house airtight by design.  The MVHR means that it always smells fresh because you are continually replenishing with (reheated) external air.

 

If doesn't matter how good the nominal design is if your builder doesn't bother putting in the roof or wall insulation where you can't see -- as many have discovered with a FLIR camera once they've moved in.  Ditto thermal bridges on steel I-beam crossing the warm / cold divide.

 

The single biggest cost component in our house was the natural local stone skin -- which was a planning requirement, as well as looking nice.  As to the near-passive performance, adding this was maybe 15% of the cost of the skin, but then again I use a 3kW inline heater to heat my water-based UFH system and our internal temp is ~ 22½°C everywhere, all year round.  Putting the water-base UFH loops in the slab cost ~$2K  and no other CH installation, rads on walls etc needed.  (The 22½°C is because a pair of OAPs like it that way.)

Airtightness has been my key research point at the moment, I am happy to spend the extra money, time and effort implementing the air tightness layers where I possibly can to ensure A, the house will last the test of time (and give us plenty of space to grow into) but B, be a thermally and financially efficient home. My other half has quite bad hay fever and now recently asthma since getting COVID!, so air sealing and active MVHR is our way to go too - Any slight breeze in summer in our current home and she's welled up to the eyes with hay fever! 

2x6 was my chosen size purely on cost, ease of movement for lifting of the walls once framed and it allows for more insulation inside the wall without losing much more floor space versus the conventional 2x3 or 2x4 timber I've seen in most commercially built new-builds recent years with the inner timber frame + brick outer leaf. I'll be doing the construction of the actual inner frame, joists, sub floor, sheathing, outside insulation etc with my dad, with internal insulation coming once my air tightness test has been completed - once thats done, I'll be adding the inner layer of insulation before the plasterboard goes on and then I can be almost certain that the outer envelope of the construction is as air tight as its going to get

Engineered or Natural stone is what I'm hoping to get on the outer layer of the house, but this will be a purely aesthetic detail after the thermal block is up as our outer leaf. I'm not really a fan of the grand-designs-esque white box in a field, no offence meant to anyone who is a fan of that look! Theres a whole host of styles in our area so I'm going to assume is no planning issue with external renders, timber clad or brick etc, but still in drawing board stages with the other half making sure we've got everything spec'd as we want, before we finally commit to going to planning permission 

Thank you for your input, I'll go read through lots of the blogs and such here, lots of reading at the moment but also lots going on with my work so I feel like Thunderbirds! All systems go 😁

 

On 13/03/2022 at 01:39, Iceverge said:

Welcome welcome. 

 

Spend £150 ish and buy a copy of PHPP.

 

With an engineering brain it's actually quite possible you'll enjoy it. Looking at the numbers (which are all just school level physics) brings amazing clarity to design in an industry that is rife with misconceptions. 

 

Thanks! Yeah I've been looking at it last few days- I'm going to buy it right before I'm off on my jollies then I can have some light reading material. My Mrs thinks I'm bonkers amount of reading I'm doing, but she spends hours reading scientific journals so what do I know 

[Russell griffiths]

If you are thinking of doing that much work yourself, then I Would look at icf. 
structure and insulation in one. 
 

[AccidentalSkydiver]

15 hours ago, Russell griffiths said:

If you are thinking of doing that much work yourself, then I Would look at icf. 
structure and insulation in one. 
 

Yeah I've looked at SIPs, I'm on the fence- one hand they'll be quick but the other hand, I have experience/training in commercial carpentry including exposed oak frames etc and a hankering to build 😁 Recently (2020 > 2021) did a stick-frame extension (20ft x 12ft) for my parents 2x4 with double top plate, XPS in the wall, 18mm ply, 150mm PIR insulation outside, 50mm air gap, traditional brick outside - its incredibly warm, frame went up in about 2 days with 45x220 joists over the top taking another day or so to get done then it was about 2 days sealing, taping, flashing, exterior insulation etc
 

Edited March 15, 2022 by AccidentalSkydiver

[TerryE]

@AccidentalSkydiver, If you don't want to go the supplied TF route, then I feel that following @ProDave's approach of buying in (mostly) pre-cut 8×2 or engineered equiv, then making up cassettes onsite for onsite erection might prove the best choice for you.  External panelvent board-out and 100mm external insulation; breather membrane, of coarse just remember to mark off the verticals lines on the outer -- this makes fitting wall ties a lot easier as they do need to be fixed the joists and not just the panelvent 🤣. 

 

If you go for pumped cellulose, Then you can internal board out with OSB3 as you go along to give racking strength, then do the pumping before 1st fit.  Of course, you will probably need an SE to sign-off on the entire structural design for B Control approval.

 

One other thing if you go this route:  go for a warmslab foundation if you can -- with integral UFL loops in the slab.  Look on the blogs and YouTube.  Search for the company that we used: MBC.  I am not saying that you should use them (though they did do an excellent job for us) -- some members here (e.g. @Stones) went this route DIY, but these videos and blogs give you an idea of what I mean.

 

Having the entire base to FFL with a +/- 2mm accuracy gives you a clean datum for cassette make-up and frame erection. 

 

2×6 vs 2×8 is mainly a structural design issue for your SE, I guess.

 

Edited March 15, 2022 by TerryE

[AccidentalSkydiver]

1 hour ago, TerryE said:

@AccidentalSkydiver, If you don't want to go the supplied TF route, then I feel that following @ProDave's approach of buying in (mostly) pre-cut 8×2 or engineered equiv, then making up cassettes onsite for onsite erection might prove the best choice for you.  External panelvent board-out and 100mm external insulation; breather membrane, of coarse just remember to mark off the verticals lines on the outer -- this makes fitting wall ties a lot easier as they do need to be fixed the joists and not just the panelvent 🤣. 

 

If you go for pumped cellulose, Then you can internal board out with OSB3 as you go along to give racking strength, then do the pumping before 1st fit.  Of course, you will probably need an SE to sign-off on the entire structural design for B Control approval.

 

One other thing if you go this route:  go for a warmslab foundation if you can -- with integral UFL loops in the slab.  Look on the blogs and YouTube.  Search for the company that we used: MBC.  I am not saying that you should use them (though they did do an excellent job for us) -- some members here (e.g. @Stones) went this route DIY, but these videos and blogs give you an idea of what I mean.

 

Having the entire base to FFL with a +/- 2mm accuracy gives you a clean datum for cassette make-up and frame erection. 

 

2×6 vs 2×8 is mainly a structural design issue for your SE, I guess.

 

I've been in constant conversation with a very good friend and ex-colleague of mine who's a SE through out the design process, He has already agreed with me 2x6 with a 600mm OC, california corners at all external corners and 3-stud U-Channels for interior walls using 2x6 for all load bearing walls are more than adequate. I'll be cutting all the framing on site to account for undulation in the foundations obviously 'flat' pads can be a nightmare with undulations and waviness. Only thing I wont be doing is trusses, I can get these made relatively cheap compared to hand cutting them on site - Joists are still on the board, I'm still considering using a I-Joist over 45x220 - mainly because they have a higher load carrying weight, lighter so I can move them myself and come in longer spans than I'd usually get in 45x220 

 

My only walls in the entire design that are 2x4 are non-load bearing partition walls between the downstairs WC/Utility and the en suite/master, everything else will be 2x6 interior and exterior. The total floor plan is less than 1780sqft not including the garage (main house 2 floors + granny flat only)

I know I sound like a no-it-all kid, who's just being awkward, but I've done extensions, stairs/stringers, summer houses, porches, dormer windows with hand-cut hip rafters etc oh and a bed because I dislike Ikea  I'm confident in my ability and between myself and my dad we have probably 40 years experience in carpentry and building (He's a chippy too, I'm just not one professionally anymore) - just now need to find some more cash and get cracking 
 

[Iceverge]

Its one of my regrets,not stick building on site. Taking a bundle of timber and ending up with a house is special.

 

I had a look at some wall buildups last night, in terms of cost only for a project in the back of my mind.

 

The most economical way to build for my target u value of 0.15 was externally osb sheathed 200*44s, AT membrane, a 44mm service cavity. pumped cellulose and rockwool respectivly, 15mm plasterboard, soundboard if you're feeling generous.

 

I like the idea of a continuous insulation layer outside then studs. Great for thermal bridging. The issue with external foam is the ludicrous price of the PIR, and the amount required to bring the dewpoint outside the sheathing. (probably a non issue with good airtight treatment taping of the OSB to be fair) Also pir shrinks, underperforms in cold weather and burns in a nasty manor. In fact if it wasn't for the headline K value (remember laboratory conditions only) and the sometimes unbelievable marketing I don't think anyone would bother.

 

Don't forget the cost of screws too. At 30-40p each long screws can add up quicky.

 

If I was building again I'd use the method I described here. Better still it can all be put together with a nail gun. 

 

 

 

 

 

[AccidentalSkydiver]

On 15/03/2022 at 19:23, Iceverge said:

Its one of my regrets,not stick building on site. Taking a bundle of timber and ending up with a house is special.

 

I had a look at some wall buildups last night, in terms of cost only for a project in the back of my mind.

 

The most economical way to build for my target u value of 0.15 was externally osb sheathed 200*44s, AT membrane, a 44mm service cavity. pumped cellulose and rockwool respectivly, 15mm plasterboard, soundboard if you're feeling generous.

 

I like the idea of a continuous insulation layer outside then studs. Great for thermal bridging. The issue with external foam is the ludicrous price of the PIR, and the amount required to bring the dewpoint outside the sheathing. (probably a non issue with good airtight treatment taping of the OSB to be fair) Also pir shrinks, underperforms in cold weather and burns in a nasty manor. In fact if it wasn't for the headline K value (remember laboratory conditions only) and the sometimes unbelievable marketing I don't think anyone would bother.

 

Don't forget the cost of screws too. At 30-40p each long screws can add up quicky.

 

If I was building again I'd use the method I described here. Better still it can all be put together with a nail gun. 

 

 

 

 

 

I was speaking to my mate who's a SE working for Manchester council on their projects, he said they recently had an issue with some council houses which are SIP built with window opening pre-formed in the panel was 40mm to the left of where it should've been, on 13 panels, and because they're not just stud walls and then sheathed they were a pain in the backside to rectify and builder ended up just scrapping them in favour of new panels all together. They also found some issue with undulation in their foundations causing gaps in some places since the edge of the pad was tapered off - he advised to go full stick frame and sheath which I think is my direction.

Have architect booked for 4th April for look over and consultation on my designs, then I've got a meeting with Amit to get him to review all my calculations and load paths for my design.. paid for with a case of beer 🍻 then its all off to planning... once all this is done, I'm about to fill my dads yard/workshop with a few pallets of timber and OSB 😁

[Russell griffiths]

I think you need to re think your joist choices, definitely 100% not solid timber, and probably not i joist either. 

Probably better with a metal web joist, it will make your life so much easier when you come to running services. 

I stick built my last place 320m ground floor. Lots of timber in that. 

 

You also need to look look at your design at sole plate level, you need to mitigate cold junction at the floor. 

 

Also so look at adding a service batten on the inside to space the plasterboard away. 

Edited March 17, 2022 by Russell griffiths

[joe90]

20 minutes ago, Russell griffiths said:

Probably better with a metal web joist, it will make your life so much easier when you come to running services. 

Maybe, but I found i joists cheaper and frankly drilling holes in OSB ( I joist webs) was dead easy.

[Russell griffiths]

1 hour ago, joe90 said:

Maybe, but I found i joists cheaper and frankly drilling holes in OSB ( I joist webs) was dead easy.

20mm holes no probs. But 110mm and 100mm for mvhr are a bit trickier if you have 5-6 pipes together. 

[AccidentalSkydiver]

The I-Joists planned are 97x220 mm engineered using glulam upper and lower beams, Maximum span per joist is 9m according to BS8103-3 / NHBC  - my biggest span would be 6m over the garage/workshop. And 100mm hole saw isn't an issue with a good saw  I did 3x 90mm in 38mm thick surface in about 70 seconds with an erbauer hole saw and arbor, clean sharp saw and a good drill does wonders (built a 2.1m long desk which is die straight, anywhere you put level is the same)

 

Using the 0.003 x 3500 (width of the living space north south) we're expecting to see 10.5mm deflection (which is smaller) that the max of 12mm deflection, but according to JJI table the deflection would be 4.27mm and an SI of 2.40 over the 3500mm span at its maximum point on hangers. I'll be using blocking/web stiffeners across the majority of the living space to give horizontal deflection capability and share some of the load there, manufacturer I spoke to can actually put in holes in the board before delivery but it would be much more difficult using solid joists (or glulam!)

 

[SteamyTea]

39 minutes ago, Russell griffiths said:

20mm holes no probs. But 110mm and 100mm for mvhr are a bit trickier if you have 5-6 pipes together. 

Why we should use large diameter pipe for MVHR, double the diameter and you quadruple the area.