Easy lean-to suggestions

[Trek]

Hi there, I'm just about to build an extension /lean to out the back of my house. Am wondering what the easiest or maybe cheapest way of doing this would be?

 

It's a straight forward skillion roof with a rough 10° pitch. With a span from the back of house wall to the front of around 7 metres (with 400 eaves)

 

I'm looking for some suggestions as I've already pulled the pin and demoed the old kitchen, now in limbo with not much clue as to move forward.

 

I was thinking a cross beam in the middle to pick up the roof of could I do away with this and just use purlins? Here the red line is the existing back if house and the blue line is proposed timber wall I will build to house the kitchen.

[Russell griffiths]

Do you mean extension, as in habitable, part of the house, or just a lean to to keep the mower under ??

If it’s the former then you need to think about everything, how will it comply with building regs, what wall design?

what roof ? 10 degrees is not enough pitch for most roof materials, there are many that go that low, but will need designing in now. 

[markc]

Russell bet me to a similar answer, first thought was something like a car port but the last bit suggests a part of the house. We can offer advice and ideas but it sounds like you need some proper professional input

[Adrian Walker]

I totally agree with the other two comments.  If you are going to sell the house in the future, make sure it is done correctly especially if it's going to be habitable.

[JohnMo]

12 degrees makes it a normal roof, less than that it's a flat roof.

 

But the third person today that wants to miss a designing it correctly stage and make up as they go along.

[PeterW]

13 hours ago, Trek said:

With a span from the back of house wall to the front of around 7 metres (with 400 eaves)

So that’s not permitted development, and demolishing bits won’t help your case with planning ! Where in the U.K. are you - as that can sometimes make a difference to rules. 

 

[Trek]

Some really great feedback cheers. Does anyone actually have an idea about as to how to erect this extension? Going through a builder or like is warranted yes but I came here first to get ideas I can put forward to an engineer say.

UK building regs don't apply here so just literally looking for suggestions in shape or process. Thanks

[ProDave]

7 hours ago, Trek said:

UK building regs don't apply here so just literally looking for suggestions in shape or process. Thanks

It might be helpful to know where you are and what regulations do apply?

[Temp]

21 hours ago, Trek said:

Some really great feedback cheers. Does anyone actually have an idea about as to how to erect this extension? Going through a builder or like is warranted yes but I came here first to get ideas I can put forward to an engineer say.

UK building regs don't apply here so just literally looking for suggestions in shape or process. Thanks

 

I think the problem is too much choice. There are numerous ways to build it.

 

Is the rest of the house timber or brick? Does the extension need to match? Are you wanting to build it yourself? Can you lay bricks? 

 

Here in the UK the most common construction methods are variations of a cavity wall..

 

From outside to inside..

 

a) Brickwork outer leaf, cavity, Insulation, block work inner leaf. 

b) Render, Blockwork outer leaf, cavity, Insulation, block work inner leaf. 

c) Brick or Rendered block outer leaf, cavity, Insulation between timber frame.

d) Timber cladding, cavity, Insulation, blockwork leaf

 

 

 

[Trek]

10 hours ago, Temp said:

 

I think the problem is too much choice. There are numerous ways to build it.

 

Is the rest of the house timber or brick? Does the extension need to match? Are you wanting to build it yourself? Can you lay bricks? 

 

Here in the UK the most common construction methods are variations of a cavity wall..

 

From outside to inside..

 

a) Brickwork outer leaf, cavity, Insulation, block work inner leaf. 

b) Render, Blockwork outer leaf, cavity, Insulation, block work inner leaf. 

c) Brick or Rendered block outer leaf, cavity, Insulation between timber frame.

d) Timber cladding, cavity, Insulation, blockwork leaf

 

 

 

Yes the original wall is concrete. It's a bit all over the shop level wise so was going to bypass by building timber wall shown in purple in pic attached. Here would sit a double top plate to pickup purlins that span from back wall to front wall.

 

I guess my question should have been more what are the standout differences in building a single span skillion roof vs having say a universal beam running through centre.

 

With the beam I'd imagine it would need to sit on and transfer its weight/load down to a strong foundation. (Instead of a standard 100mm slab with 300x200 trenches around side would probably need a substantial footing to pick up the weight .

 

Benefits I guess would be running ceiling joists into the U beam giving a flat level surface.

 

Downside i'd imagine losing height of ceiling for beam.

 

Having purlins I guess would negate any cross mid support, but downside would be raked ceiling and light fittings on angle.

 

I would just like to find the most simplistic way of doing it

[saveasteading]

5 hours ago, Trek said:

the most simplistic way of doing it

Not something that is easy to answer. Cheapest/ most durable/ most attractive/ boxings for columns and beams allowed?

 

Then we could make suggestions but you cant find  a builder who would do it that way, or at the budget.

 

In principle, for small buildings use cavity wall and timber roof, with a steel beam if necessary, then any builder can do it.

 

Do work to some approved standards please, whether they are required or not.

[Temp]

9 hours ago, Trek said:

With the beam I'd imagine it would need to sit on and transfer its weight/load down to a strong foundation. (Instead of a standard 100mm slab with 300x200 trenches around side would probably need a substantial footing to pick up the weight .

 

I think what I would build would be a "flat" roof design.

 

I'd go for blockwork walls on UK standard trench foundations (if the ground conditions allow). If there are no windows on the side walls they could easily carry the load of a universal beam supporting 3.3m timber joists. The beam ends would rest on concrete pad stones set in the blockwork ito prevent a "cheese wire" effect. The design would be validated by an engineer. If there are windows in the walls under the beam ends then the engineer may need to uprate the lintel above the window.

 

On top of the joists and beam would go "firings" (strips of wood of varying thickness to create a slight fall) then a sandwich of OSB/insulation/OSB creating what we call a "warm roof" structure. This effectively eliminates the possibility of interstitial condensation.

 

Finally you add a proprietary waterproof layer, typically EPDM or fibreglass. 

 

If you want a pitched roof you need to find a waterproof layer that can tolerate the pitch. For example at low pitches wind will blow rain up the slope and under some types of tiles and slate causing water penetration.  Otherwise the construction could be similar, just tell the engineer to size the beam and joists to carry your choice of waterproof layer.

 

Edited August 14, 2022 by Temp

[Trek]

18 hours ago, saveasteading said:

Not something that is easy to answer. Cheapest/ most durable/ most attractive/ boxings for columns and beams allowed?

 

Then we could make suggestions but you cant find  a builder who would do it that way, or at the budget.

 

In principle, for small buildings use cavity wall and timber roof, with a steel beam if necessary, then any builder can do it.

 

Do work to some approved standards please, whether they are required or not.

Yes I'll be doing it myself, wanting to go above and beyond standard code.

[Trek]

The walls can't be blockwork unfortunately. They need to be timber (reason being they can be replaced like for like) 

So I'm using old timbers to frame the walls. I can do pretty much any suggestion or ideas as long as it is simple. Materials wise I'm trying to keep costs down so basic cladding and the like.

 

Property is in regional western Australia, so although not completely exempt from certain council rules and building codes it favours the homebuilder to do his/her due diligence and erect something that meets building codes should one have to show evidence of such things in the future. 

 

The 4 walls need to be timber and the rest can be whatever is easy and cheap to build.

 

Corrugated tin is favoured in these dry arid climates. So am leaning towards timber 4 walls 6.5 C purlins 250mm @ 900 centres with insulation on top and 40mm top hats on top again and then the tin.

 

 

[ETC]

Turf?

[markc]

Anyone else completely lost on this thread?

[Trek]

On 14/08/2022 at 09:18, Temp said:

I think the problem is too much choice. There are numerous ways to build it.

 

Just give me one of the numerous ways as an example?

Just include the walls must be timber frame.......

 

Anyone have an example? Lol

[Ferdinand]

Where are you?

 

"Code" suggests North America, perhaps.

 

We can better comment if we know.

[Trek]

Take away all locations and codes etc if that's easier.

 

You have a house on the moon that you wish to build a lean to /extension out back as in the photo.

How would one go about it any examples out there?

Anybody

[markc]

As it’s a lean to then there are no ridge beams required and I would want a lot of glass so i would go Larson truss side walls for ease of insulation and services, ledger fixed to existing wall with timber I beam rafters, a couple of big roof lights and a eaves beam over the full width sliding doors

[Russell griffiths]

Ok so know you actually said what you want to do. 

I lived in oz for seven years and built a couple of places. 

So dig a trench around complete perimeter 400x400 for a footing, add formwork so you can pour the floor slab and footing in one. 

Could look for a pic but I cannot be bothered. 

Plastic membrane across the whole thing. 

Termite barrier around any pipe penetrations. 

Walls 90x35 structural grade, cannot remember the number, get the blue stuff with termite treatment on. 

Frame walls at 400 centres, ensure studs line up with board sizes so 1200  and 2400. 

Double top plate

divide long wall in half and put in a triple stud on both sides. 

Span side to side with a glue lam beam 225 x 90  or whatever you can find. 

Pitch roof as high as you can 10 degrees is fine for steel but the higher the better. 

Build a short stud wall on top of glue lam to pick up the centre of the rafters. 

Pitch rafters up from original house to front of new wall with the join in the rafters over this mini stud wall. 

Add gable ladder to both sides. 

Loads of insulation in roof. Sitting on ceiling timbers. 

Top hat on top of rafters, membrane, shines one with insulation inside, then tin. 

Crack a stubbie 

job done. 

[Russell griffiths]

 

About as technical cal as my drawings get. 

I know what I mean, and that’s good enough for me. 

[Temp]

3 hours ago, Trek said:

 

Just give me one of the numerous ways as an example?

Just include the walls must be timber frame.......

 

Anyone have an example? Lol

 

I did. See above.

[Trek]

8 hours ago, markc said:

As it’s a lean to then there are no ridge beams required and I would want a lot of glass so i would go Larson truss side walls for ease of insulation and services, ledger fixed to existing wall with timber I beam rafters, a couple of big roof lights and a eaves beam over the full width sliding doors

Cheers mark, yes I'm thinking the same. Have a 2.4 wide window to go in front wall and Hopefully snug a glass slider in also. Will have to contact engineer for size of eaves beam

[Trek]

18 hours ago, Russell griffiths said:

 

About as technical cal as my drawings get. 

I know what I mean, and that’s good enough for me. 

 

Cheers that's probably a good option also. Would you run the ceiling joists off the beam perpendicular (like in pic) or run them parallel?