Hello from a naive soul converting an agricultural barn into 4-bed house

[LionessHeart]

Hello Everyone! I've been following BH for almost a week now and am gobsmacked with the knowledge and helpfulness of all you kind people.... So here I am, hoping to learn (and in time, perhaps contribute) to this wonderful community.

 

This is a long read (sorry!)

 

We have planning permission to convert a shed into a 4-bed house in Kent. We've brought in mains water and electricity. There is no connection to gas or sewage. 

 

The barn sits on a cement foundation which we will retain. The main double-height shed is made from a pre-cast concrete structure (to keep). The 2 lean-to single storey structures on either side are built on steel beams (again, structure to keep)

 

I am in charge of this project as I have the time and *some* experience with small renovations (extensions and loft conversions). My husband's work keeps him busy and out of trouble for the most part (it's my dream to build our home that got us here!!).

We're very happy with the design drawn up by our architect. My challenge is to translate that design into a build we can afford. The QS (first pass, Stage 3 level) has come up with an astronomical build cost - more than double of what our brief to the architect was!

 

Some serious value engineering along with compromises have to be made to keep costs down. We are prepared to part-build - focus on the main shed and west lean-to, leaving the east lean-to and landscape for a later time. 

 

Overall, we want to take a fabric first approach and make the home as low-energy and sustainable as possible (near Passivhaus standards).

 

• We would like to engage a local contractor in Kent (any suggestions would be most appreciated; we live in London, 1.5 hrs from the barn so don't know the local area well)

 

• Would it be cheaper to have the groundworks done by the local contractor, then bring in a Timber Framing company (Frame Build UK?) do the build before passing it back to the local contractor take charge of the rest? What hybrid model (if any!) would be best?

 

• What professionals are essential? Our architects suggests...

                 - Building Services Engineer for heating/cooling/electrics....

                          We're keen to install ASHP (with UFH), MVHR, Solar PV (under PD, so just 9sqm), (Tesla?) battery storage. And they all need to talk to each other!

                          Can a one-stop shop (e.g., Better Planet or Total Home Environment) who supply, install, and commission be a good substitute for a Building Services Engineer?

                 - SAP consultant - we have one who can also provide Airtightness Testing if needed

                 - Civil engineer to specify the sewage treatment plant...

                          Again, can the folks at say, Graf be just as competent to specify the duct/pipe design?

                - Structural Engineer - already engaged

                - Building Regs Inspector - already engaged

                - QS - already engaged for first pass... We will likely need a Bill of Quantities before going out to tender. And wonder if using ProQuant would be more cost effective

 

So far, Roof and Wall insulations have been specified.....Is there a way to gauge how close they will be to Passivhaus standards? Does there appear to be room to reduce costs here?

 

Roof Insulation

1. Form new roof structure comprising; allow 150mm timber joists with 140 thick Rockwool Flexi insulation between joists; 12mm plywood decking; 100 thick Rockwood Hardrock insulation; breather membrane; form 50mm ventilation space from timber battens.   2  Fibre cement corrugated roof finish

Wall Insulation

1  New external wall structure, comprising; 150 thick timber studwork structure with 120 thick mineral wool insulation; 12mm WBP ply; breather membrane; 50mm metal studs to form ventilation gap; vapour barrier and 25mm Rockwood RWA slab on 25mm timber studs to internal face; 2  Corrugated cladding; 3  Timber perforated screen on 50mm studs; 4  Insulated render

 

Apologies for the long read and many questions! Any help, guidance, advice, will be deeply appreciated. Many thanks!

 

L09P-Proposed Cross Sections.pdf L08P-Proposed Roof Plan.pdf L07P-Proposed First Floor Plan.pdf L06P-Proposed Ground Floor Plan.pdf L06P-Proposed Ground Floor Plan.pdf L07P-Proposed First Floor Plan.pdf L08P-Proposed Roof Plan.pdf L00-Cover.pdf

[Thorfun]

welcome. sounds like you've joined the forum in the nick of time! TLDR all your documents (sorry!) but i've a few comments.

 

1. did you tell your architect you want passive house levels of insulation? if so, and i don't think you're quite there tbh but i haven't run the materials through a U-value calculator, then i would be going back once you've done those calculations and asking why those levels haven't been attained?

 

2. speak to many different TF companies. you specified a single company above but i would hope that you get at least 3 quotes. we got many more than that and whittled it down to a final three to choose from.

 

3. did you give the architect a budget to work with? if so then if they've designed a house that is way over budget then they've made a mistake and you'd be within your rights to get them to value engineer it.

 

i'm sure others will chime in. i'm no expert but if you read through our blog on here you can see where we're at with our journey. I might advise that you put the brakes on for a couple of weeks and absorb as much information as possible from on here by going through each forum. Also read up on some self-building books. i found Mark Brinkley's book very useful as a starter to self-building.

 

i wish you the best of luck and look forward to following your progress should you choose to share. 🙂

 

[JohnMo]

UseHi welcome

As above really, lots of comments.

 

You are being pushed to employ lots of of so called specialists and consultants none of which come cheap, and sometimes I wonder if they add value or do the complete opposite.  The more specialists the less control you have as you always fall back on the specialist.  The less control YOU have the more the costs get out of your control.

 

Example you want ASHP and UFH, add an uvc and that's the heating system done. What value did, does a consultant add?

 

You say MVHR needs to talk to PV and battery no idea why, MVHR is a standalone ventilation system.

 

You want to cut cost but you are installing a battery storage system?

 

You seem to have lots of dead space (voids) on the first floor and rooms seem to look massive, have you done a reality check on room sizes?

 

You may be cheaper doing it all with local contractors and stick build the frame work at site.

 

[Glenn]

Hello and welcome!

Couple of immediate thoughts/queries

- Whereabouts in Kent? I'm south of Maidstone and would happily recommend a builder and other trades if local

- Speaking from personal experience, converting my Class Q into full building permission gave me more flexibility with overall dimensions. My friend and neighbour took it once stage further and was able to knock his concrete frame down and replace with timber frame. Would your build more economical to start anew as opposed to accommodate existing structure?

 

Regards

Glenn

[ToughButterCup]

Welcome @LionessHeart.   Your Other Half called Richard by any chance?

 

Anyway, here goes with the advice.

• Keep the post short, simple and focussed. That way you get much more detailed answers.
• There is no limit on the number of posts you make.

For example, ask :

• Does anyone have experience of Proquant? Are there any alternatives to it? Are there any gottchas with it?
• We're hoping to build to PH standard. Has anyone got any key bits of advice?
• Is @pocster really as gorgeous as he thinks he is?

In other words, make the chunks of the  problem as small as you reasonably can. 

 

It's OK to scream on here 

 

 

[Pocster]

1 minute ago, ToughButterCup said:

Is @pocster really as gorgeous as he thinks he is?

Yes 

[Tom]

32 minutes ago, Glenn said:

converting my Class Q into full building permission gave me more flexibility with overall dimensions

 

^^^^this

If you haven't already, investigate whether your local planners would allow you to knock down the shed and rebuild from scratch. Some do and some don't it seems. Would make everything cheaper, simpler and possibly better.

[ToughButterCup]

2 hours ago, pocster said:

Yes 

 

OK, @LionessHeart, now would be  a good time to scream.

 

While you are considering if the @pocster is actually worth a scream - and not a mere snigger- , here is a reading list for you on Class Q by a really well-known author Martin Goodhall.

 

Good luck.

Ian

[joth]

5 hours ago, LionessHeart said:

 We're keen to install ASHP (with UFH), MVHR, Solar PV (under PD, so just 9sqm), (Tesla?) battery storage. And they all need to talk to each other!

Can a one-stop shop (e.g., Better Planet or Total Home Environment) who supply, install, and commission be a good substitute for a Building Services Engineer?

They can, but it can be tricky to engage them prior to tendering the main contract, but without their design input the main contractor doesn't have all the information needed to quote from.

 

As others say these thing don't all need to talk to each other. PV <-> Battery is the only crucial one from that list. Getting individual design & supply quotes for each item and providing to the main contractor is certainly an option, this is what we did and it worked out well. (They went with our quotes on all of them in the end, as they couldn't beat them. We novated 2 of the contracts over to the main contractor, for PV and MVHR, but I kept the ASHP installer directly employed by myself mostly for VAT reasons)

 

[Jilly]

Take your time (unless it’s class Q) think about if there’s a way you can live or at least stay on site in a static caravan or similar. It’s an unbelievable pain not being nearby and rent will eat your budget. 
A lot of things need to be decided on site and if a builder is presented with 2 choices, you can guarantee they chose the one you didn’t want. 
One way to manage the budget can be to get a part liveable and signed off and do the rest later

[Temp]

Make sure you understand the VAT rules before accepting any quotes. It's likely you should be charged 5% by builders and reclaim this after completion with form VAT431C. Make sure quotes spell out VAT at 5% or it can cause grief later. Any problems getting a trade to requote correctly refer them to VAT708.

Edited March 28, 2023 by Temp

[gc100]

You’re don’t need an airtight test if class Q .

the only essential people you need are structural engineer, builders (brickie and/or carpenter ), electrician, plumber and you don’t get a choice for not having a building inspector unfortunately . The rest bring minimal value and only cost imo. No idea why you’d want a civil engineer for the treatment plant? We just brought one and builders installed with correct drainage.
 

QS seem to have no grip on reality and day to day decisions made by the builder will have much bigger impact to budget and what you have negotiate at the building yards - always shop around for every time you do a biggish order- you will save thousands.

[SteamyTea]

Welcome.

Passivhaus standard is quite complicated and finickety.

Getting to the thermal loss standard is not that hard.  Just a case of reducing losses and limiting inputs.

The easy way to reduce thermal losses is to insulate and try to eliminate uncontrolled air losses.

Now you say you want to use the existing slab, how are you going to insulate it so that it is suitable for UFH i.e. 0.15 to 0.2 m of insulation before the pipework and final floor finish.

As you will be building under the latest regulations, how are you going to design out overheating (Part O)?  Many people like large windows, but they are probably a thing of the past now.  But that can save you loads of cash.

Do you have enough space for a sewage treatment system?

Where are you putting your PV if it is limited to the 9m² ground mounted limit, why not on your roof?

MVHR is, as mentioned, a stand alone system.  Forced heating, it is not, though it can be designed to be both.

If an Architect says something i.e. systems talking to each other, then start some proper research, there is probably a mate in the background that has a solution, at a much higher price.  I can fit my bike in the back of my car, and they are both transport systems.  That is where the similarities end.

 

As a general rule, a house is a very basic engineering structure, just complicated by legislation and a disjointed industry.

 

As @ToughButterCup says, break things down into simple questions, then find the solutions.

 

@pocster is a (expletive deleted).

[gc100]

4 hours ago, SteamyTea said:

As you will be building under the latest regulations, how are you going to design out overheating (Part O)

wasn’t aware of this since finishing my build 2 years ago. Ours definitely overheats in the summer due to large south facing windows but I knew it was going to. I wanted to put brise soleil Louvre externally but planning defo won’t pass due to class q amd going outside of original form. 
 

 

[LionessHeart]

a BIG SHOUT OUT to all of you for your warm welcome and for asking me to be succinct!

Note to @ToughButterCup: that was my scream

 

@Thorfun: our brief re going low-energy (not Passivhaus) was obviously not clear upfront.

                      Is there a u-value calculator for various construction materials available online?

                      Have started reading Barry Sutcliffe's book. Mark Brinkley will be next.

 

@JohnMo: Can a UVC run on electric (there's no gas). Stand corrected re MVHR. Meant to say ASHP-UFH...

 

@Glenn: we're almost neighbours (or will be!)  the barn's in Langton Green...

                      Would really appreciate pointers to builders and tradies.

                   

@Tom: this build is under full planning, but on condition we keep the concrete posts, etc. 

 

@pocster: what can I say? You're ummm... gorgeous

 

@joth: thanks for that suggestion. I've got in touch with a few Interior Climate specialists today.

                      I'm thinking of the AHSP+UFH+UVC designed by the same person, if possible. Would you be able to suggest anyone?

 

@gc100: thanks to you, I hope to save some money on our sewage treatment plant.

 

@Temp: I'm aware of the tax savings and VAT431C, but hadn't come across VAT708... it's going into my black book. Thanks!

 

@Jilly: ours is not Class Q, but I'm running against a personal deadline to move in by Aug 2024. That said, I've pushed the pause button for the rest of the week to do some reading, talking, and listening... so I can revise our plan.

 

@SteamyTea: we'll be building up the floor for the UFH, but I don't know exactly how. Have made a note to ask our architect. 

                           We do have room for sewage treatment plant and PV (there's 1+ acre). We might go for more PV with planning, but in future.

                          

 

Thank you all again for your attention and care. I'll return with short, sharp questions soon! ciao

 

 

 

 

[SteamyTea]

8 minutes ago, LionessHeart said:

we'll be building up the floor for the UFH, but I don't know exactly how. Have made a note to ask our architect. 

Don't let the Architect fob you of with a minimum level.  With UFH, because there are two temperature gradients either side of the pipes, the losses to the ground can be quite substantial.  You also have to be wary of cold bridging around the periphery of the building.

[ToughButterCup]

10 minutes ago, LionessHeart said:

....

@pocster: what can I say? You're ummm... gorgeous

....

 

Phhhhhhhhhhhh. He's going to be even more inbloodysufferable now.  😔

[Thorfun]

27 minutes ago, LionessHeart said:

Is there a u-value calculator for various construction materials available online?

i used this one https://www.changeplan.co.uk/u_value_calculator.php

 

but there are many others as well.

 

there are many knowledgeable people on here for U-values. a large number of them helped me get my head around things in this thread

take a good long read in the relevant sub-forum and you'll soon be a lot more knowledgeable!

[Thorfun]

32 minutes ago, LionessHeart said:

@pocster: what can I say? You're ummm... gorgeous

oh no! what have you done. 🤣

[Glenn]

Much as I'd like to recommend them, as they travel from 'North Kent' down to me I know thy wo't want to go further sorry. Langton Green lovely though

Regards

Glenn

[Temp]

6 hours ago, LionessHeart said:

we'll be building up the floor for the UFH, but I don't know exactly how. Have made a note to ask our architect. 

 

We have 80mm of PIR then UFH in screed and a mix of stone,  wood and tiles on top.

If building again I would try for more like 120mm of insulation. More if height isn't an issue. 

[JohnMo]

7 hours ago, LionessHeart said:

Can a UVC run on electric (there's no gas). Stand corrected re MVHR. Meant to say ASHP-UFH..

Yes the invented cylinder can be run from any heat source, with the ASHP, you would get one with 3m2 or larger coil, for good heat transfer.  You would also require a larger size as you would only be kept below 50 deg.

 

Also the ASHP and UFH have no requirement to talk to battery or PV system either.

 

Keep things simple, otherwise in 10 years when things go wrong you will be stuffed.

[LionessHeart]

Thank you, @JohnMo and @Tempfor the helpful tips!

Have a good evening.

[LionessHeart]

thank you for that tip, @JohnMo!