Viability of shell only

[SE22Reno]

I’m planning a loft conversion, rear extension and substantial renovation of a Victorian house in London, and I’m trying to sense-check whether some form of shell-only or hybrid main contractor arrangement is realistic.

 

By “hybrid”, I mean a builder taking on the main structural/building works and other agreed core items, while I separately procure some specialist packages and selected internal works.

 

About me

 

I have a day job, so I cannot be on site full time. I can commit some time to managing the project, but probably not as much as would normally be needed for a pure shell-only/self-managed route.

 

However, a close friend, who I trust, is a self-employed carpenter and runs a carpentry/renovation business with his business partner. They do not normally operate in my area and they do not have the experience/capacity to take on the whole project, but they do have good experience working on renovation projects. My idea would be for him to take on the elements he is comfortable with and help me coordinate some other packages.

 

Why I am considering this route

 

Cost is obviously one factor, but the other reason is that I have already identified a number of packages/trades that I am likely to procure separately, mostly specialist items. These include:

 

• cellar waterproofing/tanking;
• potentially cellar dig-out/underpinning, if not within the builder’s scope;
• ASHP and UFH throughout the property, by a heating specialist;
• windows and steel rear doors;
• wood flooring, at least to the ground floor;
• kitchen fitting, likely by the kitchen supplier;
• solar, batteries and EV charger.

 

I have also found a plasterer and decorator. My carpenter friend should be able to carry out a lot of internal carpentry and fit-out work, potentially including internal stud walls, plasterboarding, insulation, doors, architraves, skirting, boxing, access panels and similar works, subject of course to agreement with the main contractor and Building Control requirements where relevant.

 

On electrics, I have found two potential electricians that I would like to use. I understand that electrics probably need to be treated as one coherent package, with one electrician responsible for first fix, second fix, testing and certification.

 

My reservations

 

The biggest gap is bathrooms. My carpenter friend is not comfortable fitting bathrooms out, and I am not sure I want to leave bathrooms as something to find a separate trade for later. My instinct is that, even under a hybrid route, I would need the main builder to take responsibility for the bathrooms and associated domestic plumbing.

 

I would also want the main builder to own certain key items, such as the roof/external envelope, flat roof build-ups/VCL/weathering, main structural works, and ideally the staircase into the loft. I could possibly source a staircase specialist, but I would rather not add another separate package.

 

Generally, I do not mind that this route will cost me more time (though, as I say, I'd hope my friend can take some of this burden) but I would not want to do it if it prolongs the build by a lot (if it takes me a few extra months, that's fine, but if it takes an extra six months that would be a problem).

 

What I am trying to work out

 

I am trying to work out whether it is realistic to find a builder who would be happy to take on a defined main contractor package – structure, shell, roof/envelope, weather-tightness and selected core items such as bathrooms/plumbing – while allowing me to procure some specialist packages and internal works separately.

 

I would be grateful for views from anyone who has done something similar, or from builders/PMs who have been on the other side of this kind of arrangement.

 

Thanks in advance.

 

 

 

[Bancroft]

Thoughts from an amateur learning as I go...

We're doing similar to you but on a bigger scale.  We've contracted a main contractor to do the groundworks, slab and ICF build for a new house.  Were now preparing for phase 2 - everything else.

 

Things that have come up/been discussed with the architect and other thoughts:

 

• Check the Building Regs.  Something this big may need a designated main contractor/duty holder.  This could be you but be aware of what your responsibilities might be as a result.
• A main contractor will probably cost more but could save money by being more efficient and less stressful.  If you sequence a plumber to come in on Tuesday after the electrician finishes on Monday - but the electrician doesn't - then you're left holding the baby.  That will probably make you more likely to build gaps into the timeline which, in turn, will increase grief and nausea from the other half because things drag on so long.
• If you do use a main contractor be ready to have lots of discussions as to why you want the Heat Blaster 3000 heat pump while the MC insists on the Gentle Waft 5000 - because that's what he's always fitted.  When I told a Tesla Fan Boy electrician I would not be having anything with the word Tesla on it in my house on principle his face was a picture of 'does not compute...'
• Boundaries and responsibilities - if you're going to get different people in to do all the different jobs, how are you going to get any of them to take responsibility when something goes wrong?  The roof leaks and knackers your new MVHR - who pays for the new MVHR?  Probably easier to get an answer if one MC was responsible for the whole lot.

 

I think there are three key elements here - time, cost, risk and only you can understand the importance of each one.

We're going down the MC route because of the size of our project but there's part of me that wants to be the one in charge - because this will be our forever home but, as far as any builder is concerned, for them it's just another job to be forgotten about in a few months' time.

 

Whichever way you go throughout the contract, by all means delegate but never abdicate.  As soon as you take your eye off the ball, or allow someone else to do things in ways you wouldn't, then you're opening the floodgates to ending up with something you didn't want.

[Conor]

Bancroft had it well covered, my view as a self builder and as a project manager as a day job.

 

Avoiding a main contractor and managing the build yourself will save you upto 30% of project cost. BUT...

 

Getting trades will be tough.

You take more responsibility and risk.

It takes a LOT of time as you have to learn and do at the same time.

It's much more satisfying.

 

The key thing is to make sure roles, responsibilities etc are clearly defined.

 

"However, a close friend, who I trust, is a self-employed carpenter and runs a carpentry/renovation business with his business partner. They do not normally operate in my area and they do not have the experience/capacity to take on the whole project, but they do have good experience working on renovation projects. My idea would be for him to take on the elements he is comfortable with and help me coordinate some other packages."

 

I would absolutely not do this. Recipe for disaster. Grey lines. No cost control, you take all the risk. You'll fall out when something goes wrong.

 

Much more to it than this but I've no time to say more right now. Something that you'll soon be familiar with 🤣

[JohnMo]

 

On 29/06/2026 at 23:13, SE22Reno said:

day job, so I cannot be on site full time

Sounds like a disaster ready to happen. You can't manage a project like that, you are working when all the trades are working.  Who is managing what?

 

My advice is get someone to do the management. That doesn't need to a project manager, it could be the architect. You need someone that understands the process and understands how to engage the right people at the right time with no gaps in responsibility.

 

We did a renovation project that way and everything worked well basically a principal contractor responsible for delivery of the project, architect did the contract tenders, held progress meetings, managed timescales, managed the detailed quotes for 3rd party stuff like windows, heating, electrics etc.

 

The house build I did myself working full time at site.

 

You either take time off yourself or you get someone else to do it (from start to finish) and you do your day job.  Short cuts, expensive, take longer and cause stress and general a poor overall outcome.

[Nickfromwales]

+1 to all of the above.

 

To use a friend means you need to risk losing that friend, as you need to be ‘that guy’; if you expect him to become responsible, punctual, think on his feet, foresee issues, prevent disasters, deal with conflicts, oh and be a wet nurse (and be able to stay calm and pop back in any spat out dummy's).

 

I’ve just been on one such similar site where the client was trying to pilot the ship, whilst in work full time, and let’s just say it went ‘quite badly’……

 

Builders won’t want to principal over other trades unless they’re putting a reasonable % on everything these people do, as they are directly  responsible for 6 years after completion as the PC.

 

Underpinning needs specialist insurances too, and you need to see a copy of this, and confirm the cover is in place by phoning the insurer, BEFORE work starts. 

[WannabeBob]

44 minutes ago, Nickfromwales said:

I’ve just been on one such similar site where the client was trying to pilot the ship, whilst in work full time, and let’s just say it went ‘quite badly’……

We are doing exactly this where we are both working full time. However our jobs (well mostly my partner’s) have a great amount of flexibility to work remotely most days. It’s going OK, not the smoothest ride but also not quite disastrous. 

 

We have done a great deal DIY but also have had tradies come and do work. In all honesty, some of the most stressful times for us have been when the tradies are working (as opposed to doing DIY). It’s my partner who supervises on site most of the time owing to her work arrangements and so a lot of the oversight is by me, through her. The translation isn’t always seamless, let’s say but even then having someone on site tends to keep them on the straight and narrow..

 

I have found that on the days that we haven’t been on site during the day is when things are most likely to have gone a bit awry (dinged the doors, bashed a pipe, not done what was asked). We have been lucky that they have mostly put things right when told (it helps if there’s only one tradie at any time on site to avoid finger pointing) but I can easily imagine things having gone very differently.

 

So all that to say that it’s not impossible but it is very stressful so go in with your eyes wide open (and a steady supply of whatever keeps you calm)

 

Also massive +1 on not working with friends and family. One chap we know has been getting friends to work on his house and has caused him massive delays. 7 years on and he’s still not moved in. 

[saveasteading]

Agreed as above. All of it.

Building is difficult.

Someone with knowledge has to be in control. That has a cost.

When you say 'planning' , what stage are you at?

Presumably you have some set ideas on layout and budget.

 

Underpinning! A horrible,  messy, expensive job. Recently there have been some technical ways to support the building rather than the old ways, but I haven't researched it.   

You should do that and perhaps there is knowledge on here.

 

Perhaps do the underpinning first and preserve the building before starting to knock holes in it and excavate around it.

After that you'll know what budget remains and a bit more about your building.

 

If you have pics or reports of the structural issues then we can maybe help.

Edited 4 hours ago by saveasteading

[Iceverge]

What you suggest can be done. 

 

It'll take 4 times a long as a main contractor unless you want a gash result. 

 

 

 

 

 

 

 

[Spinny]

+1 for all comments.

As a building virgin 4 years ago I can say there is a lot to understand about how building works, and that the project management is far more demanding than you might imagine, even if you have done project management in commercial business environments.

 

Most independent trades people are small outfits, often one man bands, sometimes 2 or 3 working together.

Your job is typically small beer to them - perhaps 2/3/4 weeks work. You are likely a one off customer. So you don't have much power over them turning up compared to a builder that may give them a steady stream of work year after year after year. Even if you stay on schedule they can say I can't come that week now, will have to be 3 weeks later. Can't come wife is ill, going on holiday, cut my hand, another job overrunning, got the flu, having a baby, etc. You mostly have to suck this up. A good builder will know multiple people in each trade and have some power - I give you £80k work every year - be there monday or else.

So what you are doing is herding somewhat ferrel cats.

No tradesperson will EVER phone you. They will NEVER call and say, 'just after an update - do you need me again next week', 'just thought I'd let you know going to be out of the country next month' etc. You have to call them, always, they may not respond - for days or even weeks.

(It gets somewhat better as you move up the stack, finishing trades have to have customer relationship skills)

 

There is stuff that crops up 'between trades'. Who is going to sort that threshold gap before the flooring people come ? Too small a job to interest any tradesperson - do it yourself or get stuck. A builder can usually call in a favour to get it done.

 

You need to know what is right and what is not. Who you going to ask ? You need to be able to call an architect, or an SE, or BuildHub, or YouTube, or ChatGPT.

 

A stitch in time saves ninety-nine. Stuff done wrong is disasterous. Now it has got to be undone, then redone right. Maybe pay twice over. Everyone frustrated. So you have to be eyes on - all the time, everyday - catch things straight away - that doorway needs to be 6 inches over - that alcove isn't deep enough for the kitchen units - that reveal is well out of plumb, those pipes are in the way, etc etc. Catch it early and one spoken sentence on the day fixes it.

 

A lot depends how much quality/precisian you are after. As a self builder likely more than average. I had an architect tell me some builders in London were trying to write contract terms saying the building would be within 10% of drawing dimensions !!?!

 

Good trades peole are good, good builders are good, but they are hard to find. Find a good builder early - check them out diligently. By far the most important thing is openness and honesty - stuff happens.