Good morning Sirooris,
we faced the same questions about ~1.5 years ago when we decided to buy a single-story house with 120sqm fully basement from 1971 in our desired location in the Rhine-Main area. Our plan from the start was to completely revamp the house and redo everything including massive changes in the floor plan + doubling the living space by building up a knee wall.
We planned a lot of work ourselves, yet the crucial trades such as: new solid construction floor, roof truss/roof, gas-water-bath were commissioned to specialized companies.
To give a bit of orientation about the prices, I will write below on your list what we were charged for as far as we are through or have offers.
- Insulation of walls, basement and roof
Basement exterior insulation (bitumen and dimple membrane), drainage, revision shaft with excavation work 7,000€.
Insulation of basement ceiling material for 120sqm comes to about 2,500-3,000€, we will do it ourselves at the end or after moving in. Exterior wall insulation
- Roof re-covering
Dismantling old roof + roof truss cost 1 Saturday with 5 people, 2,000€ disposal (however with gables).
New roof truss + roof including 4 roof windows with electric blinds 46,000€
- Heating replacement
Removal of old oil tank by specialist company cost 1,200€.
Dismantling the old heating took 3 hours of own labor with 2 men.
New gas condensing boiler with solar and underfloor heating in drywall system (required due to floor build-up height in the existing building) and completely new pipes + second heating circuit for towel warmers in the bathrooms as well as new water pipes costs 48,000€
- Pipe replacement
Is included in the heating position.
- Electrical system renewal
Completely installed as own work, costs an immense amount of time: preparation by reading in and execution. Upstairs goes faster now since I already have some practice. New fuse box connection and later the connection of the lines will be done by a friendly master electrician (who luckily also checks my own work) so the price is not representative. However, I will probably reach about 10,000€ for materials including the switch program.
- Replace radiators or better yet: install underfloor heating
Heating is included in the above position. Underfloor heating in drywall system costs about 19,000€ + 2,000€ for insulation and 5,000€ for dry screed on almost 240sqm floor area. The 19,000€ is included above so here only +7,000€ to get the floor ready for covering.
- New staircase
We had a concrete staircase cast on site, which is quite cheap at 2,500€. However, it needs some post-treatment, so about 3,000€ in the end. The railing and handrail are drywall for us, the handrail is covered with Nero Assoluto as are the window sills and kitchen worktop. The marble 700€
- New windows
All new windows with electric blinds including large lifting sliding door and aluminum front door and basement windows costs us about 30,000-35,000€. According to the offer it was 28,000€ without basement windows, I only have an interim invoice so far, not the final bill.
Electric garage door with remote control about 2,000€
- Install electric blinds
- New doors
About 200-300€ per door including frame
- New front door
Is included in the window price. Ours is completely anthracite with two 80cm wide light shafts left and right and costs about 3,000€ according to the offer
- New bathrooms
We were at the sample selection two weeks ago and are still waiting for the offer. We have a reference from the same sampling company and an equally expensive plumber from the area in the family, that was 20,000€, because we have somewhat larger showers and a bathtub I better calculate 30,000€
- Re-plaster the house
I am still waiting for an offer, according to the architect's estimate 25,000€ including external insulation. But I estimate it will cost more with insulation.
- New exterior paint
Included in plastering
- Relocation / breakthrough of possibly load-bearing walls to create larger rooms
This cost us the most own labor time on the ground floor. Complete demolition, conversion, installing steel beams, partially re-bricking etc. took a good 6 months with about 20 working hours per week on average. Most costs were for disposal (this also includes removing asphalt screed etc.).
Disposal: about 10,000€, I did not calculate it exactly
Conversion materials: 5,000€
- Attic conversion
Raising knee wall 1.20 m + gables and load-bearing interior walls and chimney 37,000€
Non-load-bearing interior walls made of drywall, under-rafter insulation of roof, dwarf wall made of insulated OSB, all clad with OSB and drywall as plaster for the ground floor cost (material only) 6,000€.
Own labor in working hours 150 hours.
Additional costs included site setup with crane and scaffolding ~7,000€ for 5 weeks
Architect phases 1-4: 6,000€
Structural engineer: 2,500€
Building permit: 800€
Construction management is done by my grandpa as civil engineer, so is free. The architect would have charged 10,000€ for that.
If I did not miscalculate, even with own labor you are still solidly over 300k. But that will be due to the relatively large extension, right? Doubling living space definitely doesn’t sound cheap :)