Put a Rounded Roof on a Square House


Introduction: Put a Rounded Roof on a Square House

About: I'm a refugee from Los Angeles, living in backwoods Puerto Rico for about 35 years now and loving it. I built my own home from discarded nylon fishnet and cement.

The roof on this cement block house was made of wood and corrugated iron.  The wood rotted out and I replaced it all with a domed cement roof.  

The roof is intended to be used as sort of a mini-park area, so I made a stairway to get up onto it, and a rebar trellis over it to provide shade for people and to help keep the house cooler.  

The roof is made of what I call "nylon-cement", a combination of nylon fishnet and cement; in this case over iron rebar.   It is similar to ferro-cement construction, except that one layer of nylon fishnet is substituted for the standard three layers of chicken wire.

Here you will see the steps I went through in doing this remodeling project. 

Step 1: The Original House

The original house included two cement block buildings, the house and the "casilla" (shed).  The space between them is angular. 

The shed had a cement slab roof that was poorly made.  The rebar was set too low in the cement.  Rust had caused expansion of the rebar and destruction of the interior side of the cement slab. 

The house had a wood and corrugated iron roof.  "Polillas", kind of like microscopic termites, had eaten up the wood.  Booth roofs needed replacing. 

I decided to make a roof that would connect both structures, bridging over the space between them.
The rooftop could be used as a little park area once it had a trellis for shade over it.  The view from the roof is very nice. 

Step 2: Painting the Rebar

I painted all my rebar with primer and rust-preventive paint using a special technique I came up with.  A  piece of 3/4" diameter PVC pipe is bent to make a paint reservoir.  The rebar is pushed in one side, passes through the paint, and is scraped of excess paint as it exits by a conical silicone rubber tip attached to the end of the pipe.  The tip is formed over the conical end of a new cartridge of silicone and is trimmed with a knife to get the appropriate size hole. 

Rust can cause the rebar to expand and damage the cement, so for best quality work it is best to paint the rebar. 

Step 3: Zipper Stairs to the Roof

The Zipper Stair design, in which left and right foot steps intersect at an angle, is an original stairway design I came up with years ago.  Usually, I carve them in the ground and line them with nylon-cement.  This is the first and only set of zipper stairs that I have built in the air.   

See:    https://www.instructables.com/id/ZIPPER-STAIRS-a-new-type-of-stairway-using-Nylon/

Because I was running low on nylon fishnet, I used the traditional ferro-cement technique for the stairway and roof of the shed.  I used the standard three layers of chicken wire over the rebar, instead of a using a single layer of fishnet.  It's more work, and the assistance of another person is sometimes needed to help mash down the layers and pass tie wires through from one side to the other.  Nylon cement is a lot more user-friendly and can be done alone.

The stairs were the first part plastered, so that I could carry buckets of cement up to the roof without climbing a ladder with them. 

Step 4: The Roof in Rebar

The cement block walls of the house had stubs of rebar sticking up out of them.  The stubs were bent over some of the roof rafters to help anchor the old roof to the walls.  

I used the stubs to tie wire the new rebar to the top of the walls, so there is some continuity between the rebar of the walls to the rebar of the roof. 

Step 5: Bamboo to Support the Weight

In order to be able to walk on the rebar, to put down the fishnet and plaster the fishnet, one has to put in temporary columns.  Until the cement hardens, its weight needs to be supported, also.

The way I do that is with bamboo.  With the bamboo in place, one can use the top of the bamboo like stepping stones.   It's a little tricky, balance-wise, but it can be done.

The fishnet is held in place with wire "S" hooks and twisted pieces of tie wire. 

Step 6: Plastering the Fishnet

I mixed the cement on the ground with a shovel and carried it up the stairs to the roof in buckets.  After plastering the top side, I plastered the bottom side, leaving the bamboo in place as long as possible.  I made a saw cut toward the bottom of the bamboo to remove it since it gets locked in place by the weight of the cement.

Step 7: The "Bridge"

I felt that the section of roof that covers the area between the two structures needed some additional support.  I put a beam underneath in, more towards the center, where it was a little higher.  At the front, I didn't want to lower the height so I put a sort of beam on top.  The cut-out areas are there for looks and to help cut down on weight a little.

The white is a cement-based roof sealer.  The reddish brown is the top coat of colored cement that protects the more expensive layer of sealer underneath it.  One can "paint" cement with colored cement, instead of using house paint.  The mottled yellow walls are painted with colored cement over the original house paint.  It appears to be sticking well to the layer of house paint. 

The decorative frames around the windows are just strips of insulation foam adhered to the walls with cement and painted with colored cement. 

Step 8: The Trellis

I set rebar rings into the top of the roof for later attachment of the trellis rebar to the roof. 
A good ladder is necessary to work at the rebar intersections, tying them with wire.  The limit to the height of the trellis is just however high you can feel safe working. 

The trellis shades the house and keeps it cooler.  It also can provide food, depending on what vines you plant.  My favorites are spinach, passion fruit, chayote and zocato (juicy and sweet like a melon). 

Trellises can be converted into more cement structure, and new trellises can be added.  This kind of architecture could result in a city that more or less resembles a termite nest. 

I hope to do a "Termite Nest City" instructable eventually.  I can't built a city alone, though, so it may deal mostly with models. 

Also, a "Painting with Colored Cement" instructable is on its way. 



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    38 Discussions


    4 years ago

    This is truly amazing work!! Great job can't wait for coloring concrete

    Amazing. Zipper stairs make so much sense but never seen them before. Aren't they always pulling abandoned/lost nylon nets from the sea, where they are a menace to sea life? You have a good re-use for them.

    1 reply

    Somebody should organize the recycling of all that material. When there is demand for it, then maybe it won't all go to waste. Nylon-cement is a great way to use it.

    I am green with envy, how gorgeous have you made your part of the planet. I would LOVE to have you as a neighbor for all the vicarious thrills I'd have watching you create (you might even let me help?), I admire you and your work GREATLY! You are a classic Reassurance man.

    3 replies

    auto correct turned Renaissance into 'reassurance' ah how more perfect the world would be without autocorrect... Thinkenstein, you are a real Renaissance man. Maybe you offer reassurance to friends too.

    So, that was auto correct at work. I thought it was a humorous substitution. Either way, thanks.

    I've read about how, when pouring a dam, they must pour layer 5 before layer 4 is 100% cured. If they don't, it wont bond. How long do you wait between layers? Have you experienced 1 layer not bonding to layer below it?

    Pretty cool. Have you also considered mixing some sort of fiber into the concrete mix? I've seen mix available with short fiberglass fibers in it for strength. Maybe short nylon would be as good/ nearly as good.

    I look forward to hearing about how well your work weathers over the years.

    1 reply

    I have heard of such fiber additives, but have never used them.

    It's all holding up pretty well thus far. The unpainted iron rebar in my earlier work is probably the most problematic element, as far as longevity goes.

    I am all agog! Feel like crossing the pond, finding your wiggly-smooth houses with resident friendly path-snakes and coming for a cuppa whilst I paint you (onto canvas) not onto your skin. In the UK it's rainy but you said, cement isn't affected by water... really??? (dashes out into garden , paces all over it, cackling madly...)

    2 replies

    Visitors are always welcome, especially creative ones who know how to cackle!

    Well thanking you! I am so tired of corners. Not enough to stop me cackling though...

    wow...I had seen your zipper stairs ible...and I thought that it was pretty cool...but the scope of this project is amazing. I want to see the finished product.

    2 replies

    Is it safe to assume this structure is to code in Puerto Rico? I only wonder because I haven't seen anything quite like it, facinating...and I'd like to try this out in Canada for my own house!! I know codes will be different, but all the same, perhaps there's an alternative I can use here.

    1 reply

    Codes are a little lax this far out in the woods. Ferro-cement is accepted as a strong material, even for making ships. Design-wise, the dome is a very strong shape, and I consider the project to be a success.