Waterproof roof?

This is a simple, but fun activity that even very young children will enjoy. I did it with my 3,5 and 7 year old and they loved it, especially when it came to making it ‘rain’.

LEGO waterproofing experiment

Before starting we spent a few minutes talking about what we expected to happen and how we could make the investigation a fairer test.

We decided that the roof tiles would be the most waterproof, followed by the sticks and then grass. However we did discuss that it would depend on how many sticks and how much grass we used and that it would be hard to make the comparison fair.



LEGO house

Roof materials – we used LEGO tiles, sticks and grass

Water sprayer


Place your chosen roof onto the house and spray water on top. We used a set number of sprays to make it a fairer test.

Record any moisture inside the house.



As predicted the roof tiles kept the inside of the house dry, the grass let some water in and the sticks were also waterproof.

lego house


To improve the accuracy of this investigation we decided what we should have done was use grass, sticks and tiles up to a certain hight above the top of the house and kept that constant for all conditions.

Recording the amount of moisture inside the house was difficult. Perhaps if we’d placed paper inside and changed it for each condition we could have compared the dampness of each piece.

Can you think of any other improvements?

More LEGO posts

15 Fun ideas for Science with LEGO

More Waterproofing posts

How waterproof is it?

Which is the most waterproof roof


There are 3 comments

  1. Natalie PlanetSmartyPants

    Great idea for an experiment. I was thinking of making a “water level gauge” inside to measure moisture and putting a paper towel square inside to see if it gets wet at all. Thanks for sharing with After School Link Up.

  2. Jessica

    I might use water tinted with a little bit of blue food coloring and put a paper towel inside the house. The blue water would show up much better on the paper towel and the results of each type of roof could be compared.

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