Hidden Cave / Play Room Fort




About: I work as a Environmental Health and Safety specialist for Clark Reliance. Most of the guys there don't think I would know how to use a hammer. Sometimes, people are more than what they appear. :)

When I was a kid, we made a fort out of everything. We built a play house / fort in the woods with random stuff we found. We put together a cardboard box car, rocket ship, building, whatever. But we never had a play room to ourselves......

So, now that I have a son, I wanted a playroom or permanent fort just for him. The fun thing was figuring out where to put it and I found the perfect space, A triangular section above the dining room that is 3 feet at the highest point in the center and 11 x 14 feet overall. The problem was, to get to it, you had to crawl through attic space, over wires and open studs, and into a space with no lighting, windows, ventilation, or floor for that matter. Plus there are nails sticking through the roof sheathing..... So lets fix that.

Step 1: The Before Picture

This is what the space looked like before.

Step 2: Materials and Tools

Tools needed:

Circular Saw
Cordless Drill
Shop Vac
Jig Saw
Tape Measure
Sharpie marker
Foam spraying equipment (just hire it done)
Temporary lighting
Electrical tools
Knowledge of electrical systems
Knowledge of supporting walls


Foam tiles
Spray foam
Great stuff foam
Window weather proofing
Permanent lighting
Electrical boxes/ switches/ outlets/ wire/ breaker
Electrical tape
Wire nuts

Safety gear needed:

Safety glasses
Safety goggles
Ear plugs
Respirator - dust mask and a half face OV/HEPA cartridge model
good shoes
knee pads are helpful
and Bandaids.....

Step 3: Cleaning Out the Space

The house we live in is a century home. This means there is dust up here from 100 years ago, nasty coal dust from the old boiler, cob webs, animal stuff - we will leave it as "stuff", birds nests, mouse nests, garbage, and loose insulation.

So lets get rid of all of that and clean this place up a bit. A big shop vac should do the trick, as well as garbage bags, a dust mask, gloves, tons of soap, and a lot of time. I hired a neighbor kid for 10 hours to give me a hand. He swept stuff up, I emptied the shop vac when needed while working on construction on the rooms below, and he got some money he wanted to go on a Jamboree trip.

I used 3 sections of hose on the shop vac to reach back in here. Duct tape worked great to hold them together, with some couplings

I also used a IR remote on a outlet adapter so the neighbor boy could turn off the shop vac when it jammed, or he needed a break, which happened quite often.

Step 4: Adding a Window

I need an escape route for my son if a fire were ever to break out. Who wants to be trapped in a small space with flames all around?

So I found this great window at my local Home Depot. The window unlocks with two big handles and pivots in 45 degrees. This would give great fresh air if he wanted it. The whole window can then be lifted out and set aside leaving just the frame left and a 14 x 28 opening to escape. I can fit through it with no issues so I know my son will be able to.

I cut through the outside of the home, braced the window in place, put weather seal tape on the outside and later this year, will be putting cedar shakes on the outside of this section of the house. It never was sided before, just had tar paper on it. as it is a small triangular jut out leading to a flat roof. With the flat roof outside, my son can at least climb out onto something and jump 8 feet to the ground or my arms if needed.

Somehow I can foresee getting a phone call from a neighbor letting me know my son is on the roof again. I am going to have to work on that being for emergencies only...... 

Step 5: Adding Lighting

Who wants to be in a dark cave with no lights? Ok, well maybe there are times, but overall that isn't a great idea.

I ran electrical power into the cave area and put 3 lights in the ceiling. The switch to turn them on is right inside the access door to the chase leading to the cave. The lights are construction strand lights I had laying around. I replaced the plastic cages with nice metal cages and put in LED bulbs for low heat emissions and a cool to the touch bulb if my son decides lights are shiny and fun to touch.

The lights are plugged into an outlet box at the ceiling level. This way if my son decides to sleep in the cave area he can turn the lights off from inside the cave and use a flash light.

Step 6: Ventilation

The cave area needs a source of fresh air. I didn't want to rely on leaving the small 16 x 16 door open and hoping air would make it through.

So I bought a little bit of duct work, a vent cover, an inline duct fan, and a duct versa cap to keep my son from putting things down the vent. No LEGO men allowed in the fan.

I cut a hole in the ceiling by the edge of the dining room, ran the duct and fan, and installed a white cover on the ceiling of the dining room.

The fan was wired into a plug end and plugged into the same box as the lights.

Not only does the fan provide the area with fresh air from the dining room below, it also provides me with a way to know my son is in the cave. The fan makes noise just like a bathroom fan does. So I know the lights are on and someone is in the cave. I also know if I see my son and hear the fan running that he left the lights on when he exited the play area.

Step 7: Flooring

Half inch plywood was put down for the floor covering. It was also used to cover the floor in the crawl way leading to the cave (about an 8 foot crawl).

Luckily, I thought about doing this project when I had the ceiling open and under renovation in the room under the crawl way attic part. I was able to put a bunch of plywood in 2 foot and 3 foot wide sections up above for when I could finish the cave prior to the drywall going back up.

The plywood was screwed down to the floor joists to secure it in place.

A hole was cut for the ventilation duct to to through. The Versa cap on the duct makes it look a little industrial which I like and keeps the LEGO men alive and not blended by the fan.

Step 8: Insulation

Closed cell spray foam insulation was installed by a local company called Pureseal. They installed the foam 5 inches thick on the ceiling of the cave and 4 inches thick on the walls. They also sprayed the walls and ceilings of the 3 rooms I had under construction below in the home as well at 4 inches and 2 inches respectively.

After informing the guy of what I was hoping to do with the area, he covered the studs as well with the foam to make it look more like a cave. They did an amazing job. And I have many other studs not covered for termite inspections in the future.

The insulation basically makes the room like a large Styrofoam cooler. the insulation value is about R- 30 on the ceiling, which is much better than the R-1 that was in there with less than 1 inch of blown in insulation when I started.

Having gone through the summer with the heat, when it was 85 outside it was about 90 inside the cave area. But this was without the ventilation system on. With the system on, it is constantly pushing the 77 degree air into the cave from below and it cools down nicely.

Step 9: Painting

I don't think I have ever been in a cave that has spray foam colored walls. So I needed to paint it.

I thought about what I wanted to paint it with, even researching the fire proof paints used for foam. The problem with that concept was this room is in the top of the house. Nothing above it would catch fire before something below it did. If the fire got through the floor and reached the foam, the smoke in the room would have already done the damage to anything living inside. So the high expense of coating the foam in the fire paint didn't make sense. As well, the rest of the foam in the rooms below were already covered with drywall. They would not be coated either, so risk analysis said don't buy the paint.

I instead chose to try and paint it with something that would be rubbery to protect the foam a bit. I made the wrong choice. I tried spray on bed liner, Rustoleum Leak Seal, and the rubber spray for under vehicles. The Bed liner spray and under vehicle spray both had a chemical in the propellant that caused the foam to weaken as it dried. The finish cracked funny. So those were a bust. I thought the leakseal was an option. I put 10 cans of it up on the ceiling as my test spot worked great.

First, I didn't do my job and read the ingredients. It contained toluene. In a small space even with the window open, the fumes were not good. This was the first time in my life that I screwed up with painting in a not well ventilated area. I had shut the vent fan off due to not wanting paint smell in the rest of the house with my wife being pregnant at the time.

Toluene is funny. You are perfectly fine for 5 minutes. then at 5 minutes and 1 second you get a head ache, and at 6 minutes it becomes harder to coordinate movements out of an area which I had to crawl out of. Toluene hits quick and shouldn't be messed with. Sadly I could have prevented it as I had the proper half face respirator with OV/HEPA cartridges. I just didn't use them. 5 hours of a head ache later, and feeling like I was going to throw up the whole time, I decided I wouldn't be so stupid on the paint again and used the respirator for the remaining 8 cans I had to spray. The 10 cans only completed about 1/2 of the ceiling. At 10 dollars a can I waited another month to buy some more.

I found though that after a few weeks, the foam started to weaken a bit just like with the other two products I tried. It didn't give me the rubbery feel I wanted at all, but was kind of crispy. I switched to just flat black latex paint and painted the whole thing with my Capspray HVLP spray gun instead.

So lessons learned. Don't spray toluene based things in a small space, and the 3 products listed above are not good to cover foam with, at least for the first layer.

Step 10: Flooring

Who wants to lay on a hard plywood floor. That doesn't sound fun. But foam tiles on a floor. Now that is something I could crawl around on.

I purchased the 2 foot foam tiles with Microban technology to hopefully prevent the growth of anything on the foam. I know at some point there will be food left on the tiles or a cup of juice spilled.

The tiles interlock together and look and feel great. I used two colors, grey and green to give some contrast. The tiles are 1/2 inch thick so the floor is padded nicely.

Step 11: Finished Cave Pictures

Here are a few pictures of the finished product. The cave came out great. It is a bit difficult for me to climb in and out of it but I am 29, not 5. Now I just have to wait a few years for my son to be old enough to go into it. He is currently 4 months old....  Until then, I might just have to go up there to escape every once and a while. Could be a good place to take a nap. Sadly, I can't hunt in my city even though I border a metro park. I saw two deer walking across the back yard yesterday while working in the cave area finishing things up. It would have been a beautiful shot through that nice window.

Hope you enjoy the room design and maybe you can build one yourself someday.

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    75 Discussions


    5 years ago on Step 11

    Fantastic. I new even before the last page that your son must be "new". I'd guess probably your first, as well. Congratulations. I can read the pride you have, every time you wrote "my son". I know exactly how that feels. Cool cave. Keep being a good dad.

    3 replies

    Indeed he is my First. His name is Asher. I almost made the green foam into an A on the floor but then decided if I had another child, they might not understand why they didn't get a letter in the cave. :)

    Haunted SpiderJulsL

    Reply 3 years ago on Introduction

    It is a rather unique name. I like it a lot. Glad to hear someone else has an Asher out there. He actually doesn't know about the cave yet. It is a secret at the moment. I plan to show him when he is 3. Right now he is a bit over 2 and although he likes to climb on everything I want him to be a bit older before letting him play in there. Don't worry, he will spend hours in there shortly ;)

    The Rambler

    5 years ago on Introduction

    Awesome project! I love how much planning and thought went into each aspect (i.e. insulation, ventilation, fire escape, etc.). As I was reading I suddenly thought, "But what if he leaves the lights on all the time?". Lo and behold the next paragraph down you had a plan covering just that situation.

    I feel like a ladder or some kind of low structure to jump onto is a good idea for that 8' jump, but other than that I don't get all of the "Oh no, fire!" people. Houses are flammable, period. Matches aren't good for small kids to play with, period. This doesn't change if the foam is flammable. The wood it's attached to is flammable anyway. The important thing in any room of the house is having a good fire escape and being able to use it.


    5 years ago on Introduction

    I love the project and the results, but as a foam installer, I do take issue with not covering the foam. Unless the foam company used Class A rated foam on install(doesn't appear so, Class A is almost always tinted for ease with the fire inspector) it's not up to fire code. The common requirement is for a 15 minute fire barrier. The best thing I could suggest is to add another layer of paint, making sure that it's an intumescent coating, like CP5901 INSL-X Fire Retardant Paint (INSL-X is a benjamin moore sub-brand).

    1 reply

    Thank you for the suggestion on the paint. You are correct that in order for the code to be correct, I need an intumescent coating or even 1/2 inch drywall. But that is if I try sell the home and use the space as a selling point of usuable space. It doesn't meet the codes for a usable space in so many other ways as well, ceilings at 7 feet, HVAC run to the room, etc. It is covered by a barrier though when the little door is closed as the area below and walls surrounding have a coat of drywall. Also being a century home, the majority of the home is not up to code. With these in mind, and knowing the rest of the rafters are not coated either but connected to the crawl to the cave, I chose not to paint on the intumescent coating.


    Great job! I have done similar things with foam, both for my kids and in my hotrod shop. One option for coloring the foam and for the rubber feel you were after is duplicolor bed armor. It is a black, water based paint that dries rubbery to the touch yet very strong once it fully cures, which it does basically through evaporation of the water. It also has chunks of kevlar in it, which help give a rugged look and a texture that isn't slippery. I have also strained/pressed the kevlar out and sprayed just the base color on foam, which worked well. Your boy should be using the cave now, any chance for an update?

    1 reply

    Thanks for the advice on the bed armor. I will have to try that out. The black paint has held up fairly well so far. As for an update, both my son (now almost 5) and my daughter (2.5) play in the space all the time. The picture attached is of my son discovering the tunnel/ cave. He had a hardhat on and lantern to check out the new area. I sat inside and filmed it in the dark until he got to the light and turned it on to see his face. He knew I was in there so he wasn't scared, plus he had his trusty lantern. He loves the space and continues to play in it.

    day 1.jpg

    1 year ago

    You could make an epic Goonies lego diorama in there.


    3 years ago

    Oh I love that you built this for your son before he was even crawling haha <3


    4 years ago on Introduction

    I love that! Once I've tried to make one of [url=http://interbeds.com]bunk
    beds[/url]but I could do it. But I love your project and everything.


    Thanks, I am trying to be a cool dad. Right now though, I am un cool if I walk out of the room to get something, or set my son down because I just can't hold him any longer. Ah, an 11 month old will do that to you :)


    5 years ago on Introduction

    Fathers like you make the rest of us to look lazy and deadbeats! Congratulations on your project. :-)


    5 years ago on Introduction

    Nice idea but as your adventures confirm this looks like a toxic play house. Apart from your comments about fire exits for your son I wonder what the foam will be giving off in the way of fumes?

    I don't want to be negative, I liked the concept, when I looked at this it looked cool, I actually thought the ceiling was some kind of paper mache or recycled cardboard of some type and the floor was the paper packing you see sometimes in the bottom of fruit boxes, made from paper pulp.

    Out of interest did you research any of these options?