ᐅ Adding an Additional Floor. Use the Same Brick as the Ground Floor? Insulation of the Existing Structure?

Hello,

I am planning to add a story to an L-shaped bungalow next year. The house has a full basement, and both the basement walls and the ground floor are built with solid pumice concrete blocks. Initially, the plan was to raise the existing hip roof, build an upper floor, and then reattach the roof. However, since the roof was originally constructed with narrow rafters and is not insulated, I was advised to remove it entirely and install a new double-pitched roof with thicker rafters and insulation.

Now, some questions. The architect suggested using 24 cm (9.5 inches) calcium silicate blocks with 10 to 12 cm (4 to 5 inches) external thermal insulation made of polystyrene.

I mentioned that there is a lot of negative feedback about external thermal insulation systems and that the additional costs only pay off after a long time. The architect responded that the savings on calcium silicate blocks balance out the cost of insulation, so calcium silicate plus external thermal insulation equals the price of a well-insulated solid block.

For aesthetic reasons, the upper floor should not overhang the ground floor, so external insulation would also have to be applied to the existing ground floor walls. Is this advisable? The architect said that since exterior work is necessary anyway, the extra cost for insulating the ground floor would be only around 15,000 EUR.

When I consulted a construction company and a structural engineer, both advised against using calcium silicate blocks and recommended 24 cm (9.5 inches) pumice blocks, like the existing structure. Both also recommend full external thermal insulation.

On the other hand, I have read and seen that construction company owners and similar professionals rarely equip their own homes with façade insulation. However, the builder I spoke to showed me the insulation on his own house — he uses external thermal insulation. What is really recommended? Supposedly, over 90% of new buildings have external insulation.

Regarding the type of block, pumice and calcium silicate are similar in price. Pumice offers better thermal retention but transmits sound more easily, while calcium silicate blocks sound better but are colder.

I would truly appreciate any advice and tips.

Can really no one say anything about this? Even if someone doesn’t have answers to all the questions, at least when it comes to insulation, almost everyone who has built a house should be able to contribute something.

We built using calcium silicate blocks and an external thermal insulation composite system (ETICS). The advantages of calcium silicate blocks are their high bulk density, which provides good sound insulation, high thermal mass (helping with summer heat protection), and strong structural properties.

For your project, I would also suggest considering timber frame construction. What does the structural engineer say about the possibility of adding an additional storey?

What is the U-value of the ground floor exterior walls? How much benefit would extra insulation provide? Is it even necessary?

I don’t know the U-value of the ground floor. The walls are made of pumice blocks with drywall plasterboard on the inside of the exterior walls. The windows are old double glazing, some have lost the gas fill, and some are fogged on the inside. The building was constructed in 1980.

The question is whether there is any reason not to use a different type of block on the upper floor than on the lower floor, or if it’s better to build the extension using the same type of block.

I do not want a timber frame construction. I want everything to be solid masonry.

HausbauWI2016 schrieb:
The question is whether there is any reason not to use a different type of brick or block on the upper floor compared to the lower one.

One argument against mixed construction methods is often the different thermal expansion properties (for example, exterior walls made of calcium silicate brick, interior walls of aerated concrete). I can’t judge how valid this concern is, but I consider it exaggerated. In general, mixed construction methods are quite common: solid construction and drywall are usually combined, and different materials are typically used for walls and ceilings. Therefore, I don’t see any fundamental objections to using a different type of block or brick on the upper floor.

What should especially be considered (and this forum cannot do that—it requires someone with detailed knowledge of the building) are:
- The building’s structural stability
- Space (whether having thicker walls is acceptable or if slim walls are preferred)

You can find the appropriate U-value for your type of block or brick in freely available tables online. You need to know the block’s characteristics (is it hollow?) and its density (which can be determined from a core sample if necessary). Are you familiar with online U-value calculators?

Ultimately, the building needs to follow a comprehensive concept, since exterior walls are only one part of the overall heat transfer surface.

As far as I know, the existing structure uses 34cm (13 inches) hollow pumice blocks. They were not filled on the inside.

Regarding the wall thickness, 24cm (9.5 inches) blocks plus 10cm (4 inches) insulation are planned. The architect said it should be built with calcium silicate blocks. The structural engineer said I could also use pumice blocks. He mentioned that the advantage would be that the blocks are identical to those used in the lower part of the house and cost about the same.