ᐅ Seeking Help with Conservatory Extension

Hello everyone,

I would like to have a conservatory / sunroom added to my house. I am looking for people who would like to share their experiences regarding the foundation slab and partition wall.

Here is my situation: When looking at the location of the future conservatory from the front, we want to build a wall towards the neighboring property to attach the conservatory to. I was thinking of a cavity wall with 12cm (5 inches) blocks, insulated on both sides with about 5cm (2 inches) of insulation, and plastered. The wall is supposed to slope and extend approximately 15cm (6 inches) above the roof structure.

1. Is 12cm (5 inches) thickness of cavity blocks sufficient for a wall height of about 235cm to 265cm (7 ft 9 in to 8 ft 8 in)?
2. Is 5cm (2 inches) of insulation enough to provide adequate thermal insulation? What material would you recommend?

The foundation:

I have read and heard a lot about this, but in the end, I am still unsure. My idea is as follows: Under the patio, where the conservatory will be built, there is a garage ceiling approximately 50cm (20 inches) below. So I was thinking:

I would make a strip footing with concrete formwork blocks from the hardware store. From the garage ceiling upwards, I would layer it as follows: first one layer of Isover Styrodur with 40mm (1.5 inches) thickness to protect the garage ceiling waterproofing, then the formwork blocks set on top, reinforced with 10mm (0.4 inches) steel rods and filled with screed concrete. Then I would excavate the patio to the required depth for my substructure and compact the soil. The layers from bottom to top would be:

1. Isover Styrodur 100mm (4 inches)
2. Concrete floor slab 150mm (6 inches) thick (does anyone know what kind of concrete I need here?)
3. 2mm (0.08 inches) PE foil as a vapor barrier
4. Dry fill (such as Knauf or similar) up to the desired height
5. Fermacell board
6. Maurexin Austrotherm UNIPLATTE 10mm (0.4 inches)
7. Electric underfloor heating embedded in leveling compound
8. Tiles

By the way, the floor slab should be separated from the house wall with 5mm (0.2 inches) of Styrofoam and support the wall on the other side on the formwork blocks, forming a kind of load-bearing L shape.

Is this setup acceptable or completely overkill? I would like to use the conservatory with insulated glazing and a non-thermally broken structure during winter as well. The wall would be built on the floor slab.

I hope you can help me.

Best regards

You’ve asked quite a few questions :-)

First, I have a few counter-questions because I’m not entirely sure I understand the situation yet... Is the conservatory going to be freestanding? Should one wall of the conservatory act as a barrier between you and your neighbor?

So, if I understand correctly, you will have only two walls with glass panels—one wall facing the neighbor and the other facing into the house?

If that’s right, it means you don’t need to spend a lot on insulation in general; average insulation should be enough since heat loss is mainly calculated based on the glass surface area. The orientation of the conservatory is also an important factor.

For insulation material, I would suggest either rigid foam or hemp, depending on your ecological preferences... Hemp is almost as effective, but more environmentally friendly. A thickness of 5 cm (2 inches) should be sufficient due to the relatively small glass area.

The wall thickness seems adequate in any case, as it doesn’t need to bear any load. Since the wall isn’t freestanding, the height shouldn’t be an issue either, I think.

Before we get to the foundation... have you already obtained all the required building permits / planning permission?

hi

I would agree with using hemp, as you can run into some moisture (condensation) issues in the conservatory during winter, since the sun causes everything to evaporate and then when it cools down again
phew

but that is exactly why hemp is excellent as interior insulation
rigid foam boards are probably similar

how about the ventilation?

First of all, thank you for your interest.

The house is an end-of-terrace house, facing west. Obtaining the building permit / planning permission should not be an issue. For ventilation, slots are planned along with a roof exhaust fan.