2 Storey Side Extension with Lift!

[Chris0655]

I have always enjoyed reading about the projects on this site, and have found them a great source of information and tips. I vowed that if ever I was to do my own project I would share it with everyone. So, here goes…..

My 2 Storey Side Extension with Lift

The builders are due to arrive on site in 2 weeks. To help visualise the works I created a Google Sketch Up model of the existing house and the planned extension. Here is the front quarter view…

This image shows the existing house as it stands at the bottom and with the planned alterations at the top. And here is the rear quarter view…

The house is set on a hill, so the garage floor is just over 1 metre below the ground floor level.

Basically, we are going to replace the flat roof above the garage with a pitched roof and add a small rear extension. This will give us an extra 45 m² of living space including the following:

• Home theatre/sports bar
• Lift in its own shaft for disabled access
• Breakfast room
• An enlarged utility room
• Dressing room off main bedroom
• Walk-in wardrobe

We also going to make some other modifications in the house:

• Replace the existing warm air central heating system with a combined warm air and radiator system.
• Add some basic home automation
  
• Add a TV distribution system
  
• Add some Wi-Fi access points

I will add some plans and further pictures in the next post. I would be happy to answer any questions and hear any feedback.

 

[Chris0655]

So, here are the front and rear elevations:

There is one slight problem with this elevation that I can't seem to solve. We have a really nice picture window on the 1st floor above the front door, but if we extend the new pitched roof over the porch, we will have to drastically reduce the size of the picture window. I thought about creating a light well and leaving the window intact, but that would mean that we would look at the inside of the porch roof every time we come down stairs. This could get annoying. Therefore we will probably stick with reducing the size of the window. If anyone has any other suggestions I would be interested to hear them.

The rear elevation is slightly incorrect as we have now swapped the large ground floor window for some French doors.

 

[Chris0655]

Looking at the internal layout....

Ground floor:

First floor:

And a cross section through the lift:

These plans have been modified very slightly, but are pretty close to what we want to achieve.

 

[RossyH]

Looks good Chris. Keep us posted on progress.

 

[Chris0655]

We have now moved from Greenwich Mean Time (GMT) to Builders Site Time (BST). By my calculations BST is approximately 2 weeks behind GMT. Basically the builders haven't started yet.

The good news is they are actually finishing off another job, so hopefully the same rules will apply when it comes to finishing mine. And, they do intend to start within the next few days.

Here are a couple of pictures of the site before anything happens to it. From the front...

And the view from the rear....

Don't worry, the barbecue has been relocated to a secure location so that it can be properly used over the summer.

The two-week delay from the builders has actually worked out well. I was reviewing the structural engineer's calculations over the weekend and found a very significant error... The sort of error that can lead to a house falling down! More to follow in the next post.

 

[GeoffJ]

Interesting project - I do have a question - more out of curiosity

Why are you pitching the roof over the garage at the 1st floor? it is this that messes up the picture window

You could simply extend the profile of the 2nd storey out over the garage and keep the roof over the entrance area flat.
It would mean that you could keep your existing picture window intact and the head room will be improved in the media room.

I can't tell if it would allow enough space for the lift ?

Nice house!!

Geoff

 

[Chris0655]

Thanks Geoff for the comments.

When I was originally working out the concept for this extension I investigated the approach you suggest, and other variations. Something along these lines:

However, this evolved into the current arrangement. The reasons for this are:

1. Because our house is on side of the hill there is a danger that we could dominate our neighbours house, downhill to the right, with a full height 2nd storey extension. So, I wanted to keep the side elevation as small as possible to minimise the visual impact on them, and any loss of light. We get on very well with our neighbours and they have been fully supportive of this project. I can honestly say that if they had objected, we would not be proceeding.
   
2. One of the Croydon Council planning policies is that extensions should be subordinate to the main building and not create a terracing effect. They interpret this to mean that the facing wall of the extension should be 1.5m back from the existing building’s main wall. This would drastically reduce the size of the room above the garage.
   I had a pre-planning meeting with Croydon Council and discussed this with them at length. I felt I could argue my case if necessary, but concluded I could achieve what I wanted with a more subordinate proposal. In the planning decision, this approach was recognised, and cited as one of the reasons for approval.
3. The new roofline gives us more floor area in the media room above the garage. The restricted head room will only impact on the front 60-80 cm of the room. Even at head height, the usable floor area is bigger than simply extending out from the existing front wall.
   
4. I don’t like flat roofs and am very happy to see the back of all mine!

The compromise is that we have to encroach on the picture window. But so be it. I also would have liked a balcony.

Regards
Chris

 

[GeoffJ]

Hi Chris0655

Thanks for the explanation.

You said "the facing wall of the extension should be 1.5m back from the existing building’s main wall" - it is true that the side extension must be subordinated at the front - but this can be 1 brick (10cm). the balcony whilst interesting is too messy - but the rest of the design is good. I understand the need to maintain good neighborly relations.

if you really want to loose the flat roof then then the picture window would need to go anyway.

Geoff

 

[Chris0655]

I have received some good suggestions regarding how to tackle the problem of the pitched roof over the porch obscuring the picture window. So, thanks for that.

I think my preferred solution is to put a recessed flat roof behind the pitch along the whole front of the main house. Like this...

From ground level, it would appear as if the pitched roof extends to the front wall...

I shall just have to live with having a bit of flat roof! Which is worth the trade-off to keep the picture window intact.

The roof will be a little bit more complex to construct but the additional costs should be offset by not having to replace the picture window.

 

[Chris0655]

I mentioned in a previous post that I discovered a significant error in the structural calculations. The sort of error that can lead to a house falling down, and that is no exaggeration.

For some reason, just a gut feeling, I have always been uncomfortable with the supporting steelwork as specified. There are 5 steel beams which will support the extension. As shown on this the layout:

The main structural support for the new extension will be provided by beam 3 which sits on 2 vertical posts. This beam will support the internal wall for the room above the garage, this wall supports beam 1, which takes half of the load from the roof. Basically, beam 3 and its posts carry a lot of weight.

Each beam has about 3 pages of calculations in the structural engineers' report, which look like this:

So, I had a few hours to spare last Sunday evening and decided to teach myself structural engineering. What I discovered was that the structural engineer had completely overlooked the fact that beam 3 supports an internal wall, as well as supporting beam 1, which in turn supports the roof. Quite an important job! He had only allowed for beam 3 to support the media room floor.

I double checked my calculations and sent him an email. Within the day he had reproduced the calculations with the correct loading. But no hint of an apology. Spot the difference between the original and revised calculations. I have added arrows to make it easier for you!

The difference in adjusted load on beam 3 is about 30,000 Newtons, or approximately 3,000 kg i.e 3 tonnes.

Looking at the buckling resistance of the originally specified beams, this would probably be enough to cause them to fail.

None of this was picked up by the "experts" - the architect, Building Control, and the structural engineer, who is BSc CEng MStrucE qualified.

There is a good chance that if I had not picked this up, at some point in the future, I would probably have a pile of rubble instead of an extension.

The moral of this post is "go with your gut feeling", and don't blindly believe the experts. He hasn't sent me his bill yet. I think a large discount is in order.

 

[Chris0655]

And, so it begins.....

Whoaa! Where's the patio gone?

Easy boy, it will be put back, but a bit higher to make it easier for disabled access. It will be at DPC level, with a French drain all around.

 

[Chris0655]

And this is where the rear extension will sit..

 

[Chris0655]

Week 2.

The back corner of the existing house has been removed to make way for new footings.

The building inspector wanted the footings deeper than the 1m already dug so that the footings sit on virgin clay.

The footings at the far end are now 1.3 m deep.

New foul water drainage will be laid around the outside of the extension for the waste from the kitchen and utility rooms.

 

[Chris0655]

Work has also started inside the garage to prepare the pad footings for the steelwork.

The building inspector wanted pad foundations 1m x 1m x 1m deep. But the excavations actually uncovered very good footings already in place for the garage wall. We are going to see if we can use these as part of the pad. The bottom of this hole is solid concrete, about 40cm below the garage floor.

 

[Chris0655]

The footings for the rear extension went in today.

The guys did a brilliant job and barrowed in nearly 6 cubic meters of concrete; 1 and 1/2 lorry loads; 12 tonnes, in 3 hours.

Hard graft. At least that's how it looked from were I was sitting!

The footings complete and the rain started. Helps keep the concrete moist and makes it stronger.

The shuttering at the far end raises the return footing 200mm to give extra strength to that section which ties into the existing build, and will support the beam across the back.