Existing building to extend, how to model it in Sketchup?

I am planning an extension to an existing house, so I need a model of the existing house in Sketchup to start with…
The existing building is L shaped. How should I build this in Sketchup. Room by Room?
Two rectangles attached, and fill the rooms in after?

How much of the existing house do you really need? I wouldn’t model more of it than I actually needed to show. As for how to model it, that depends on what you need to show and how you need to show it. I’d be inclined to start with the perimeter of the existing building, or at least the end of it where the extension will go and flesh it out with only enough detail to do the job. Then add the extension. Make sure you are using groups and components as you go. Stay on top of correct face orientation, and I wouldn’t bother with adding any materials until the modeling work is complete.

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its a bungalow, will be adding another storey to it, and a ground floor extension with extensive remodelling of the bungalow (half of the rooms stay, half go)

What I said still applies. Model only what you need. Don’t add more detail than is absolutely necessary. Might be easier to start with simple as-built save that and then modify it to show the additional building.

so don’t do the rooms , two rectangles to represent the L shape?

It depends on what you need to show. Think about who you are doing this for and what information you need to communicate. Do the existing interior walls come into play? Do you need to show where interior doors are? Or is there a chimney breast you need to worry about? There’s really too many unknowns for us to tell you exactly what you need to model and what you don’t.

SWMBO isnt so hot at visualising the possible changes so need to show visual image of before and possible after configurations/solutions.
Also want to share ideas with Architectural technoloigists so that we can remotely agree the way forward (lockdowns/covid will continue into 2021 and remote working is here to stay , having visual images will help enormously

So there’s your audience. As I said, model to show what you need. I wouldn’t model as if each room was a separate box. Draw the floor plan for at least the parts of the house you need to show and raise the walls. Add the windows and doors at least as openings and go from there.

thanks Dave, very helpful, have used sketchup before , but may need to refresh some skills using you tube tutorals.

Good luck.

You might want to go through the tutorials at learn.sketchup.com

You will need to model a fair bit of the ground floor if you are adding another storey. Apart from anything else, you need to understand how the staircase joining the two will work. But there may also be a question of understanding which ground floor walls can be used to support the floor. Then there may be drainage issues, ie. how stacks affect things.

My approach would be to carry out a measured survey of the existing house. Then draw the walls on plan and extrude them up to ceiling level. Draw openings on the external face of the wall and push/pull them to form through openings. Make the whole thing a group. You can add window and door details but only if important. Position and size of openings may be all you need.

Similarly, you can add a ground floor thickness if important. I presume the roof will disappear, so you now have the basic structure that will exist before you start to extend. As @DaveR says, make sure you keep grouping things as you go to make sure they are not “sticky” and they are in logical amalgams.

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thanks Simon.

Newbie to Sketchup and trying to make my wall lengths exact , but finding I can only get to within 5 or 10mm of the actual measure value with the mouse and moving walls and using the visible dimensions .
Must be a way to input the exact wall lengths?

Start the movement then let go of the mouse and type in your exact dimension and hit enter.

@Box has answered your question but I would also say that trying to get more accurate than 5mm on most building work is pointless. You won’t be able to measure to that level of accuracy without specialist kit and even if you could, you would find walls would be slightly out of square or parallel. And builders cannot build to a greater degree of accuracy either. So a professional draftsman will assume that a wall that was intended to be square or parallel is even if it isn’t, unless it’s so far out that you can’t ignore it.

Hi Simon,
agreed, not too many builders will be accurate to 5 or 10mm. A SIPs structure might be though.
Also these drawings are not for builders but for SIPs suppliers to get a ROM cost for the purposes of budgeting.
Would like to start accurately at the beginning to help ensure the my costs are based on correct measurements.
When it comes to the actual work, will have the building professionally surveyed from which technical drawings and precise panels can be manufactured


So if the building will be more accurately measured in due course, you don’t need it to be that accurate now. Especially if it’s just for pricing purposes.

If you do need/want accuracy, you need to input the dimensions and/or use inferencing.

unless one is a bit OCD

admitting nothing mind you

Nobody should be recommending blurry dimensions.


I have to disagree.
Norris knows the dimensions and wants to draw to size. Let him already draw precisely. It is worthwhile to learn the right method from the beginning, as it is much more difficult to get rid of bad habits later.

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