How much does a house weigh?
I’ve been asking this question ever since I began pondering the option of a floating house. If it weighs too little, then every time a resident jumps up and down on the balcony, the house will rock noticeably. If it weighs too much then flotation becomes a problem.
I’ve been looking at the house we’ve already built and thinking that it shouldn’t be too difficult to calculate its weight:
One of the main design goals I had with this house was to eliminate all hiding spaces for mold, dust, and critters. As a result, all of the structure is visible from either one side or the other for walls, floors, roof, etc.
So finally, on Saturday, Praew and I brought a notebook, a tape measure and a scale to this house and did a reasonable calculation of the weight. Here is what we did:
Note that I am currently only interested in the weight above the foundation.
- Take samples of every piece of wood, fiber cement board, and metal used in the construction of the house and measure and weigh them to get a the unit weight of each of the materials.
- For the large metal beams sitting directly on the elevated cement footings under the house, we counted the beams and measured their lengths directly. Same thing for the vertical steel support columns.
- For other supports and surfaces for floor, walls, roof, etc., we calculated a weight per square meter and then measured the number of square meters.
- For windows and doors, we just assumed the walls were continuous figuring the weight of the wall was a rough estimate of the weight of the window or door. (I suspect this is a slight overestimate, but I’m not trying to be perfectly precise here.)
This calculation isn’t 100% accurate, but I’d guess it is within 5%-10%.
The total we came up with was about 11.6 metric tonnes. This breaks down to:
- 1562kg of steel structure below the floor
- 1946kg of interior flooring
- 1267kg of balcony flooring
- 356kg of steel support columns from floor to roof (actually a few of the outdoor balcony ones are large reused wood beams, but I didn’t have samples to measure and these would have been metal if we didn’t have the wood around)
- 2924kg of wooden walls (including interior and exterior walls)
- 183kg of large steel structure to support the ridge beam (including the ridge beam)
- 2335kg of rafters and purlins
- 952kg of roof tiles
- 100kg of bathroom floor tiles
Hopefully I haven’t left anything out, but I’m pretty sure it is complete enough.
Interestingly, if you split the weight up between house and balcony and then divide out by floor space, the house itself weighs about 125kg/m^2 and the balcony weighs about 50kg/m^2.
So for the dimensions of the floating house I am currently imagining (8m x 4m house with 2m balcony on all sides) this comes out to about 7 metric tonnes. This doesn’t include the floor of the loft including support and doesn’t take into account the fact that we are planning to use a lighter construction design but it does provide a starting point for discussion.
In particular, I am looking at ways to reduce the weight of the roof which accounts for about 3.5 tonnes or about one third of the weight above, in order to lower the center of gravity. I don’t want the house tipping over in the water during strong storm winds. 8-
Additionally, one needs to take into account furniture and people. Just rough numbers, I figure we may reasonably want to have about 1 tonne of people (if we have a some guests over) and about 1 tonne of furniture (refrigerator, wooden counter tops, couch, tables and chairs, a bed, a piano, etc.).
For reference, a 9 metric tonne floating house including people and furniture would result in a 2.4x flotation to weight margin if we went with the 22 cubic meter displacement packed 12″ PVC option. On the other hand, if we went with the packed honeycomb of 200L plastic drums with 63 cubic meters of displacement, this would result in a 7x flotation to weight margin.
All of these are still very rough calculations at this point, but it seems promising so far. Nothing ruled out as too unreasonable yet.