Structural plans for 2 storey extension

[RichA]

My planning consultant has advised me that we need more articulation at the rear of our house extension (this would to reduce the perception of bulk) to assist with a successful planning approval. This is a bit of a set back in agreeing a final design for planning submission.

As such, we are now considering an extension that projects a little further at the side of the rear (say by 1m), than in the centre, with an infill and sloping roof at ground floor level. I like the aesthetics, however, I am concerned that this is structurally more complex.

I would be very grateful for any thoughts/advice on:
(1) Feasibility & complexity?
(2) Required location of supports>
(3) Size (and cost) of RSJs required?
(4) Other considerations?

Blue=keep existing, Yellow = remove some/all, Red=new, Green=RSJs???

Extension (red) is 14m wide x 4m deep.

 

[^woody^]

Surely the whole point of an extension, and the primary consideration, is the internal space and what you need from it internally, and not just having a big block on the back of the house?

I can't see anyone being able to answer your your questions though, and would suggest that it is the whole point of you using a designer in the first place.

ie it is totally pointless someone drawing you a plan that is not feasible to build, does not know how the thing is to be supported, does not consider the cost of building his design, and does not consider everything that he needs to.

 

[RichA]

Thanks, Woody.

The designer did the first plans (4m 'square' extension) and these seem to meet our spacial requirements, are feasible to build, etc.

However, we obviously need to get it through planning and are taking advice on articulation to break up the rear aspect to reduce perceived bulk. And I quite like the new look. It sacrifices no space at ground level and the loss of a little space on the first floor is minimal concern.

I suspect it is feasible and not too complex, but was seeking some reassurance. So my main concern is the sizes/quantity of steels required (versus a flat back, which doesn't need the inset 1st floor supported over the kitchen).

[truth is we are unsure that our designer will be able find a good solution and I am therefore exploring options, this is variant of another project I saw with some sympathetic articulation]

 

[freddiemercurystwin]

Yep gotta agree with woods, all of this is best aimed at your designer, if you feel he is not up to it find another.

 

[RichA]

Apologies, I probably should have posted more with my initial post but (unwisely) wanted to keep it compact.

There is a design plan for the interior. This is the ground floor plan (the study will go where the dining room is, a playroom where the study is, and we don't need a dining room).

I like it; and think it meets our requirements for the interior (larger, more open space).

But I am now looking to modify/articulate the rear elevation to help it through planning as my planning consultant has some concerns that the council will think it looks too bulky. Therefore, after some research, I have found a potential design mod which articulates at 1st floor level but keeps the space on the GF (where I want it most).

So (I think) I have an interior & exterior design I like, and wanted to check that it is reasonable structurally before pushing on and incurring lots more costs (designer, structural engineer, etc).
[Particularly supporting around A-C and E-F)

 

[wessex101]

A 2 storey rectangular block across the full width of the back of the house would look like crap.

The fact that this was only queried by your "planning consultant" would suggest to me that your designer is a bit out of his depth. (The apparent use of lettering stencils suggests they are also about 20 years behind the times).

Time for a new designer I think.

 

[RichA]

This was the proposed design for the rear elevation, plus 2 small dormers.



Here is a reasonably square rear that I think looks good (albeit mine would be more like the left than the right).

 

[wessex101]

You really can't see the difference between those two images? If your designer was trying to replicate the photo I suggest you take him down to Specsavers.

Look at the ratio between wall and window areas and the pattern of the windows, roof ridge height, materials and textures, the small details such as the decorative band course and the canopy. All designed to turn a big ugly overbearing monolith into a harmonious and well proportioned home.

The drawing is crap (he really pushed the boat out with his window designs), the photo of the house is beautiful (but that modern extension is bloody hideous). I say again...time for a new designer. I look at that plan and I get a 1980's Barratt "Executive Homes" on an estate in Milton Keynes vibe. Nice.

Is this the point when you tell me you did the plans?

 

[RichA]

Appreciate the comments. That was designed by my Architectral Designer. We have submitted for PD, but also plan to do a further full app to make some changes/improvements.

Re: Plans being Barratt like - I take it that is not a compliment Does that include interior layout - anything in particular?

I haven't shown him that pic, but had/still hope that I too can have my own version of a harmonious & well proportioned home. My new proposed modification for the rear was inspired by this pic.
(but I accept that we would also need fenstration changes to get there).

 

[RichA]

Firstly, thanks for the advice so far. A bit of a wake-up call on this project in terms of importance of aesthetics & design and not just utility. I had been focusing on the planning process (in terms of trying to overcome council imposed limitations to size), without looking ahead to what the end result may be.

This thread encompasses 2 points in my mind:

(1) Exterior
- I have taken the comments on board and have contacted a few designers with a brief to improve to the external appearance. Going to cost a few pennies, but worthwhile if it avoids building a 1980's Barratt Executive Home!

(2) Interior Layout
- I still wish to consider the current G/F layout as I think it meets my requirements and I have not been presented with better options. But if this is not possible structurally then I will move on and try and find a solution that does work. I have simplified the G/F plan, to highlight 4 potential beams:

6.5m supporting the rear of the existing building, presumably the load will be reduced as new roof will span to new rear,
6.0m supporting possible inset rear wall/roof
4.0m supporting the 6m beam
2.5m supporting existing/original side wall

Grateful on thoughts whether this is feasible, so that:
if yes, I can pursue with designer, structural engineer, etc; or,
if not, what the main limitations are so that I can liaise with my new designer

Or do I need a structural engineer to survey and assess?



Many thanks.

 

[^woody^]

TBH, I think you are asking too much of anyone on here to tell you if its feasible. That would take some more detailed analysis.

When designing something like this , the designer should be sketching his ideas and at the same time thinking about how it can be built. So the big spans for instance, would require the designer to consider if they can be supported and by what - can narrow beams be used, do they need a pier or column, what about the bearings, how will deep beams fit in the floor or above and below. Its all that stuff.

This needs to be done at the same time, else what you find is that you have some marvelous looking plans that just cant be built or will bankrupt you, or just get altered when an engineer looks at them.

Its the same for the roof, only here its a bit more limited for options, but the key thing is that you dont want to have to be doing maintenance every few winters or replacements every few years, because the designer has done some ill-thought out detail.

 

[RichA]

Ok, thanks. Should be fine to have piers, columns, etc so it maybe that this ground floor layout remains on the table, but as I am now going with a new designer who is going to put forward a couple of options as plans & elevations so I will see what designs they come up with (and will ensure they are eminently buildable...).

 

[^woody^]

Just stress to the designer that he needs to consider beams and building it.

If you want beams to be hidden in the floor and not below it, tell him. Likewise if you don't want piers or large piers. And for roof valleys and drainage to be thought about in terms of maintenance.

In fact, come to think of it, the CDM regulations require him to consider building operations and materials in terms of safety in the building work and future maintenance - lifting stuff and future access. And you as the homeowner employer may share that responsibility too.