Haha no..it was on Mumsnet and you helped me with it :) but had some more ideas since then and thought I might post here too.

Tell me more about the extension. Where are the windows, doors, rooflights etc? A sketch would be useful.

The extension doesn't exist yet :) we are really looking for design ideas. I have bookmarked some extension ideas in an Ideabook, but its essentially the typical layout with bifold doors out to the garden. I'd like there to be lots of light, so probably a vaulted ceiling with skylights.

We do want to add more bedrooms by extending into the loft but I think funds will not allow for that just at the moment. Essentially we would like a front reception and library/study room, then a utility and WC and coat/bootroom area, and open plan kitchen reception. An extra room as a guest bedroom/craft room would be helpful.

We will mostly likely turn the ensuite back into a small bedroom (which I suspect it was originally) and with the loft extension the house would be worth a lot more than we paid. The garden is 90' plus and we'd only be adding about 2m once the conservatory is gone so that is not a concern. We don't intend to sell for 20 years until the chidren have left home!

The neighbours (other side of the semi) have extended sideways, to the rear and into the loft so it is possible to do a side extension, but wouldn't be within permitted development.

What an exciting project to undertake. My advice would be twofold. I love the idea of the open plan with the bifold opening to the garden, but I would section of the utility area and wc and definitely add a shower/wet room in to your plans. Although the rest of your space is planned as open, I would suggest being clever with a bit of zoning.

With open plan living there is a risk of it being noisy to live in as they invariably include the kitchen (all hard surfaces) and generally have a tiled or wooden floor throughout (more hard surfaces). With all these hard surfaces the noise of general family life reverberates off every hard surface and can become quite overwhelming.

Also, with your main living room planned for this space, with open plan you can't get cosy as there's so much space to fill.

Zoning and partitioning in a clever way can be the solution. Obviously you won't be putting solid walls around each space as this defeats your aims, but by creating 'rooms' with glass walls or open double sided shelving or using your furniture helps to designate a space. These methods still allows the light to move throughout the entire space but helps to create different areas.

To resolve the noise reverberation you need to add soft absorbing surfaces, such as sofas, curtains, rugs etc. These are items that you will typically be using in the living room area but you may need to consider them in the kitchen end too. It is important to remember that as a family this space will be used by all of you at the same time, potentially in different areas and you don't want one person's activity to intrude on someone else's.

It sounds like an amazing project. I hope it all goes well.

The house has poor flow through the ground floor, every room is a corridor. I would consider demolishing the garage to create access to the long garden and building a house better suited to your husband's taste at the bottom of the plot. You could then fence off the house at the front and let it, and use the income to pay most of the mortgage on your house which would be have the benefit of being sheltered from traffic passing and could make better use of the aspect than the current house.