What did you do well?

[neversay]

We are planning a substantial extension to a detached house that includes a two-storey side-extension and wrap-around across the back. This will add further space to the kitchen/dining room at the back of the house, as well as utility room, wet room, garden room/office, master bedroom and en-suite. It will also hoover up lots of issues with the existing house, such as re-roofing, replacing the staircase, levelling the garden, etc.

I'm trying to work through all the use-cases and design features we would like in order to avoid regrets like "I wish we had" or "I wish we hadn't". It's far better to feel like "I'm glad we...". So my questions are:

On reflection, what did you do well? What decisions did you later appreciate? Which did you later regret?

There's a whole host of areas we need to consider:

Planning (e.g use architects or just technical drawings?)
Design
- Layout
- Architectural interest (cladding, vaulted ceilings, other features)
- Good Lighting
- Sound proofing
- Decor
- Clever storage (bikes, recycling, tools, etc)
- Gadgets (smart home, cabling, etc)
Materials
- Build quality
- Tiling or panelling
- Flooring
- Windows/glazing
- Roofing (pitched or flat, tiles etc)
- Fixtures
Eco features
- Cleaner energy (and the end of gas)
- Improving air quality
Value for Money
- Reducing costs (avoiding unnecessary costs, cheaper substitutes, cheaper sources)
- Good investments (spending on quality, longer-term pay-offs)

Any nuggets on what you later came to appreciate, or regret, however small would be very helpful indeed.

[dealtn]

Underfloor heating def plus. Too few lights in kitchen negative. Over spec and don't try and save small amounts of money that will be negligible over the lifetime's use of the extension.

[Mike4]

Building work usually costs twice your highest initial estimate and takes five times as long.

Most people I meet who have had an extension built, say "Never again, we'll move house instead next time".

[Urbandreamer]

Kitchen & Utility rooms. You just can't have enough plug sockets. I got stange looks asking for two double sockets above each worktop. It wasn't enough!
I did insist upon a proper extractor cooker hood, as in one that extracts the air.

Network cabling. I didn't get anything done about this. You realy should think about the possibility when doing new construction. However a better idea is propper conduits. That way cabling can be upgraded later. Don't forget TV and or satelite cabling. Even with network cabling consider WiFi repeaters. You may not need them depending upon construction, but planning costs nothing.

In the living room I also installed 5A lighting sockets. This enabled standard lights and my christmass tree lights to be turned on and off at the light switch. Although modern christmass tree lights use plug in PSU's that won't fit.

USB charging sockets are a nice to have, but you could go overboard. A plug in charger may work faster and in the long term be less issue.

Phone extensions, alarm, etc?

Since you are talking something that big, consider insolation. Do you want relatively small windows and lightweight materials. That would make sense if it is north facing. Rapid to heat, while smaller windows lose less heat. Possibly you want big windows with dense materials in the floor and walls if south facing. Thermal mass will absorb solar gain during the day and keep things warm at night. Screening could be used to limit thermal gain.

Under floor heating? Heat pump?

[dealtn]

Building work usually costs twice your highest initial estimate and takes five times as long.

No it doesn't. Unless the definition of "usually" is different in your dictionary.

[Mike4]

Building work usually costs twice your highest initial estimate and takes five times as long.

No it doesn't. Unless the definition of "usually" is different in your dictionary.

Oops, having spent the last 50 years of my life in the domestic building industry, I must be mistaken in what I thought I saw happen on a regular basis!

Or maybe you missed that word 'initial' in my post.

[dealtn]

Building work usually costs twice your highest initial estimate and takes five times as long.

No it doesn't. Unless the definition of "usually" is different in your dictionary.

Oops, having spent the last 50 years of my life in the domestic building industry, I must be mistaken in what I thought I saw happen on a regular basis!

Or maybe you missed that word 'initial' in my post.

Nope, I saw it.

I can't match your 50 years, being only 51, but I have yet to be involved in a project 10% over budget, or delayed beyond 20% of the initial timeline. Several have come in below budget or time.

Frankly I'm surprised you have been in that field so long if 2 times and 5 times are "usual", as it's not something I have ever seen.

[greenrobbie]

We had similar work done on our semi-detached house. We employed an architectural technician who specialised in this sort of domestic work to oversee the entire project, as well as draw up plans, prepare detailed schedule of works, shortlist contractors and conduct the bidding process. This was our best decision. It enabled us to get a very reliable and honest building firm as the main contractor, and not have to mess around scheduling the work of various sub-contractors. They also, on the whole, employed very good sub-contractors.

As work went on, we needed a great deal of additional work in the original house and in the ground. We also found that we were choosing the more expensive option almost every time we needed to make a decision on materials or methods. A predicted 16 weeks schedule turned into 40 weeks, and, including everything, including replacement soft furnishings, the final cost was close to twice the original estimate. I had anticipated that the project would overrun both on cost and time, and in addition to an identified 15% contingency in the costings, I had squirreled enough money to cover all the additional costs - all of which were authorised by us before being incurred.

Other things that worked out well: Very large number of power outlets in every room, especially in the kitchen. Inclusion of a number of USB charging sockets. Installation of a large shower cubicle (as opposed to something only just large enough). Creation of a store room in the house so the living rooms don't look over-cluttered with our possessions.

Regrets: The living room floor proved to be in a very poor way, not capable of patch repair. So it was dug up to a depth of 10 inches to install proper insulation and a solid, damp-proofed concrete base. I wish that we had the same work done in the dining room and hallway, although they are in perfectly acceptable condition. I thought that we had a good, realistic grasp of the chaos and mess created by a substantial building project. Ha ha ha! How wrong we were. Unless one has a background in the building trade, or been through this before, it is almost impossible to appreciate how messy it is. Looking back, two years after the project was finished, we love the new improved house and it all seems worthwhile. There were dark days in the process when it seemed never-ending. Thank goodness the builders were honest and likeable, and we had a good project manager to hold our hands. I don't think we could face ever going through that again.

Hope this helps
greenrobbie

[JohnB]

If you plan to get an electric car, consider a charging point and 3-phase power to the house with the other electrical changes. Solar panels and air-source heat pump, but the latter may need radiator changes throughout the rest of the house.

Rainwater diversion for plant watering.

Holiday plans for periods without kitchen or bathroom

[neversay]

Thank you for all the great tips.

I was going to mention replacing the floors to full insulation with wet-loop Underfloor Heating (in the downstairs) as an example of what we did well on the internal renovation. Additional ports are for the extension. In a previous thread we covered the future replacement of gas boilers, so I'm interested in future-proofing for future energy solutions like heat-pumps and solar.

It's fair to suggest the pros and cons of extending versus moving. We are in a very desirable location. The build cost will be around £130k which will be more than covered by the increase in property value and utility it brings. The design will make a great family home but the ground-floor will also accommodate wheelchair access, ground-floor living and being a granny flat. So our next is likely to just be a downsize in 20+ years, ceteris paribus.

The house is East-West facing, with the side-extension facing South but no plain windows that side as it overlooks a neighbour. The roof will be suitable for solar. The rear extension is circa 10m long and West facing but will have sun on it from late morning onwards. It will be glass along the back (issue of sliding doors versus bi-folds?) and at present I'm tending toward a pitched-roof and large velux (safe to rule out flat roof and lanterns?).

Yes to sockets, network cabling and LEDs - good lighting is important and I have struggled with it in the past. We will include power ready for car chargers and plenty of external sockets/lighting (inc. for seating areas and a possible garden office). Likewise for water supply for front/back and perhaps possible irrigation system for some raised beds. As our TV is via the internet, do we need TV cabling?

For the long-term, having a house that is easy to maintain and with low overheads will be a good result. I want to have a complete 'bill of materials' and to make purchase decisions ahead of time, rather than being up until 2am researching showers when an instant decision required.

I confess that I'm not looking forward to the pain of the build and have already deferred it a couple of years due to workload and bereavement. If we don't proceed soon then 6 and 9 years our kids will be off to uni, so will miss some of the benefit. (Plus it all assumes we aren't entering into a Covid-19 depression etc. - in which case I'd rather keep the £150k in my bank account!)

It's a good point about architectural technicians. We did talk to an architect a few years ago with the request to come up with design options, instead he just came back with detailed CAD drawings of a design that plainly didn't work. In my experience builders, and the crowd here, have seen hundreds of extensions can know what works/doesn't work just as much as an architect who is more interested in making a 'design statement' than the use-case for post-walk washing a dog without getting muddy paw prints everywhere.

[dealtn]

safe to rule out flat roof and lanterns

We went flat roof and lanterns. No regrets. North facing and this allows for a large amount of natural light. We extended out 4m and pitch roof wouldn't have worked anyway, but no regrets at all and love the look.

[neversay]

We went flat roof and lanterns. No regrets. North facing and this allows for a large amount of natural light. We extended out 4m and pitch roof wouldn't have worked anyway, but no regrets at all and love the look.

That's useful to know. Ours will be 380cm so the pitch does get tight. Our nextdoor neighbour has done the higher flat roof and lantern but with covid I have yet to see it from the inside. It sounds like modern flat roofs don't suffer from the maintenance issues of the ones of old.

If you plan to get an electric car, consider a charging point and 3-phase power to the house with the other electrical changes. Solar panels and air-source heat pump, but the latter may need radiator changes throughout the rest of the house.

Rainwater diversion for plant watering.

Holiday plans for periods without kitchen or bathroom

Yes to the car charger straight from the main input/fusebox, although I need to understand more about the 3 phase power.

I was considering irrigation, but hadn't yet thought about rainwater diversion systems (beyond a water butt). Good tip.

The holiday plans are a good point too. I'm hoping we can minimise the internal disruption to when we knock-through, although it will 'undo' work that we did last time - like a new beam in the kitchen and possible replacement of the cheapo engineered wood flooring we put in last time (mindful that it could get ruined). Covid willing, I need to cost-in my wife and kids staying with family in the US for a month while the dog and I hold fort. Another cost but lower stress all round!

[DrFfybes]

Frankly I'm surprised you have been in that field so long if 2 times and 5 times are "usual", as it's not something I have ever seen.

But if the works hadn't taken 5 times as long he'd only have been in the field 10 years

Paul

[Urbandreamer]

Yes to the car charger straight from the main input/fusebox, although I need to understand more about the 3 phase power.

I'll try to simplify it. A standard, single phase, domestic supply is limited. Usually at about 100A. I advise checking what you have and upgrading if less.

You can get fast chargers that run at about 7KW on a single phase, but they are not as fast as if you could use a 22KW or more charger.
Unfortunately you really need three phase if you are going to draw that kind of power.

A Nissan Leaf can have a battery capacity of 60KWh. The 7KW charger would charge it from almost empty to full in 10hr. It would take an entire day if using a 13A plug. The 22KW could provide that charge in a about 4 hours.

Getting three phase might not be cheap. It depends upon how much digging is required and how far the cable has to go.

Multi-phase power has many advantages, but the cost of upgrading is often prohibative.

[bungeejumper]

As mentioned, getting enough powerpoints into the kitchen. We were very well advised to work out how many we'd need, and then double it. That's how we finished up with 14 double power points and eight fused spurs in a 22 foot room.

Putting power points into the side of a kitchen island. Saves a lot of trip hazards, and helps with tray heaters, food mixers, and soft romantic lighting (in a kitchen diner). Yeah, I know, I know.....

Making sure the damn doors were wide enough! Nothing is more annoying than miserly doorways and narrow passageways, when an extra 20 cm of width would have made the whole space feel more comfortable. And the house more attractive/valuable.

Taking the utility room seriously. Double drainer, thought-through plumbing, masses of storage, and a wet 'n' muddy area.

Mistakes: We forgot to turn the house round by 180 degrees, so we didn't have the option of a south facing conservatory.

Probably unavoidable: A very long (20 foot) outflow pipe from our shower enclosure, which passes under two other rooms before it reaches the outside wall. So the drop is just okay, but only just. It needs flushing with washing soda once a month to keep all the attached plugholes in other rooms sweet and aromatic. We could have avoided the whole problem by keeping the shower exit pipe completely separate from all other plumbing, right the way out to the drain. We could also have installed a pumped drain, but we decided that would be overkill. It probably wouldn't have been.

Top tip from daughter: Install a full outdoor power outlet for the hot tub, barbecue space etc. If you don't want them, somebody else probably will....

Top forgotten advice from daughter: Get the garden drainage fixed before you lay the patio.

BJ

[Howard]

We all have a different approach to life and you may be interested in my experience for what it’s worth. I considered a modest extension to our home in around 2002. Adding a third bathroom, enlarging the main bedroom with walk-in cupboards etc. It would have been built over an existing single storey room with no problems accessing soil pipes and plumbing so, apart from getting the roof lines right, a pretty simple project. I had a written cost estimate of £40k. Like you, we live in a desirable location and have lots of space around us.

Mrs H was against the idea as she reckoned it would involve a lot of disruption. I liked the idea because I reckoned it would add a lot of value to the house. However, to ensure that I was considering all the options I asked Hamptons (who had sold us the house) to visit and give me a valuation. I was upfront in suggesting that I wasn’t thinking of moving straight away and was considering an extension.

It was a very interesting discussion. The valuer was very open and professional. She said that they would love to sell the house (again) and, given a sensible price, it should be very easy. Her price suggestion was significantly above what I was expecting. When I asked how much extra I could expect, if the extension was completed, she was very definite in stating that it would probably not add any value to the house. Prospective buyers would probably not pay more. Because it was a fairly modern house and well-designed, its value would not be enhanced by an extension.

This made me reflect on the project. Instead we had a new kitchen. And paying the £20k bill for this made me realise that to achieve the quality of extension I was planning would probably have ended up costing me north of 80k!

So I decided to accept Mrs H’s view and instead of building, invested the 80k in shares (which have now grown to more than 240k!)

And I have watched several neighbours building extensions like the one you are proposing which have cost them around £250k each. One, which completely remodelled a house like mine, adding a further beautiful bathroom, luxurious garden room and lots more space, taking a year or more to complete. A few years later the house was sold for virtually the same price as it would have if unmodified.

And tomorrow Mrs H and I are going for drinks to our near neighbours who also have spent a fortune on adding underfloor heating, a garden room with lantern, extra bathroom and extended utility room. We’ll admire the improvements but I can’t get out of my mind the squalor which these affluent people had to live in for six months of hell while the builders grappled with lots of unforeseen minor problems. I’m pretty sure their initial estimate was for around 150k but the eventual bill must have been twice that. Mind you the project manager was able to afford a new Tesla Model S!

So, like Mike, I’d always advise moving house rather than extending.

And of course, since 2002, our children have gone to Uni, got married and moved away. Leaving us in a nice large house with only two bathrooms!
And the £240k has been more than spent helping the children buy homes.

regards

Howard

[AlumniLawn]

You ask a rhetorical question "bi-fold or sliding doors". We went for sliding but I regret not going for bi-fold.

Maybe if I had gone for bi-fold........

[csearle]

Read some excellent things here. As an electrician I would say that you should make sure that the trades have the infomation they need early enough to do their stuff early on. As an amateur cook I would say make sure you have good bright under unit lights. Whoever mentioned 5A socket outlets switched from the normal switching positions is a wo(man) after my own soul. Unless it is a recent build have the fuseboard changed out for one with an RCBO for every circuit. Everything else (regarding this specific point) is, frankly, [expletive deleted].

Chris

[Mike88]

The best thing I did was hire a decent architect who came up with the most imaginative design. Before that I engaged a technical drawer but dispensed with his services as the design he came up with involved a flat roof which was not what I wanted. Fortunately the architect operated as a one man band and wasn't that expensive.

[PrincessB]

I agree with many of the points made, especially the one about architects being out of touch with reality or on the flip side, ones who just draw the same plan over and over - Admittedly it goes straight through planning but the design is hardly interesting.

If the extension means a new kitchen, start planning the kitchen straight away and by the time work is about to start you'll have a final design which incorporates everything from:

Space for you or the prospective buyer to fit that really big fridge/freezer
External ventilation over the cooker hood (already mentioned)
Enough light - Kitchens should be really bright when cooking and additional dimmable lighting helps to set up the ambiance.
Off the peg kitchen units tend to use 15cm multiples for the units so you can design the room to fit the kitchen not the other way round.
Worksurface - I know there are all sorts of materials at all sorts of cost but they all have drawbacks. Stone is expensive and can be porous. Stainless steel can scratch. Wood can be a bugger and can age very fast. I'd say that if in doubt, see if you can find a bog standard budget surface (The plastic over particle board) which will offer easier upkeep than some very expensive options and it is cheap to replace if you burn it.

Watch out for thermal gain, if you face into the sun you could find the room gets very very hot. Velux windows can be fitted with heat reflective blinds that work very well, you can also buy retractable blinds that sit on the outside of the window that block 75% of the heat ingress and in Winter they retract into the frame.

If you have a lot of glass facing the sun you could consider anti sun glass, the upside is that it really works, the downside is you don't get the thermal gain when you want it in winter. You can use external awnings or plantation shutters but I would steer clear of those blinds that sit inside the cavity of the double glazing as I can't see them working for long.

Think hard about bi-fold doors and ask how many times each year they would be opened and quite why you need to open the house up that much. Bi-folds work in a really big room as you won't need anything near them, in a smaller space where you might want a pot plant or chair near the windows how about French doors that open outwards and fold and lock back on themselves - Not so stylish, better to live with and less likely to go off trend.

Where I would consider bi-folds a great idea is to partition rooms when required to allow maximum flexibility of house space and to avoid being too open plan all the time.

Have a really good think about where the light will get into parts of the house that are going to get buried inside the extension - Also think about how much time you would spend in those areas and how light they need to be. There is a big trend towards having a statement double height entrance way to impress guests! Don't know about anyone else, but I don't spend a great deal of time in the hall so why should I waste money on an area where I spend a tiny fraction of my time.

You might find a few extra windows in the older parts of the house more beneficial.

To close,

Watch a lot of property shows with a very cynical eye and you'll soon see what is on trend and what makes sense and what is a waste of money. Think of the current gang of designers as the children of the people who sold punters avocado bathroom suites in the 70's, they don't care if it makes sense for your lifestyle, they just want you to want it because everyone else does.

For kitchen design, try a copy of two of Caterer and Hotelkeeper - They disect commercial kitchens and detail the way the work flows in the kitchen space. It might sound a bit over the top but a complicated idea made simple is going to work better than a kitchen designed by someone who is better at CAD than knowning how to plan things for greatest efficiency.

Last point, if you want a log burner go for it, but see if you can get one with an air inlet pipe as well as a chimney - This will confuse some retailers but it mostly isolates the unit from the room and you won't get draughts in every room as the device pulls air in through every nook and cranny.

Regards,

B.