Hiding a steel truss with landscaping

And... anyone know who I'd talk to (or web site), to find out if I can bring plants into STX?

ENG: PM danieljude on this board.

Breadfruit trees grow tall and fast. Where is the cistern?

Thanks East Ender.

Exit Zero: The cistern is under the house (but free standing). The house will be roughly 80 ft long by 20 feet deep. The 80 ft long dimension runs along the crest of the hill, so if you're looking at the back of the house you're looking at 80 ft of truss. From the front of the house (up on the crest) you probably won't be able to see much of the truss work, and that will be easy to hide. Given a 20 ft setback, 20 ft of house depth and a roughly 1:2 steepness, I end up with a truss that is roughly 20 ft high in places. So, if I can get trees, mid-size shrubs, etc around the base of the outer perimeter of the truss, then I think I can effectively camouflage it (break up the straight lines in places, and completely mask in others). Any suggestions of specific trees I should look into? I think Crape Myrtles (the 20-30 ft Natchez) would really work well, but it sounds like they maybe don't grow well there. I wouldn't do a hedge of Crape Myrtle, but a mix of various size material, in a few layers or waves. So, I'm thinking of something like 3 groups of palms as an anchor, with some mixed in Crapes (of various sizes), a bunch of Bougeas and hibiscus to fill in some lower levels. Add a few Bananas... I'd really like some tall (40 ft) trees that would end up shading the back (north) deck that will be 20 ft above ground in places.

My breadfruit trees are 2 years old and 40' high - you can trim them and they will spread out - big broad leaves - Also some varieties of bamboo get that tall fairly quickly as well. Palms are slow growers - or very expensive if you want one over 15' - Mangoes grow slow too and will invade a cistern or septic with the roots. African tulip may be a good choice for flowering tree. If you can find a copy of 'Flowering trees of the Caribbean' illustrated by Bernard and Harriet Pertchik -Rinehart and Company publishers 1951 it has some good ideas.
A free standing cistern? You mean like a fiberglass tank? Concrete cisterns are the norm here and provide a solid foundation for the house. You don't need to provide much shade to a N facing deck usually. I don't know anything about Crape Myrtles - have you been to the Ag Station?

Hi Exit Zero,
Thank you so much for the excellent suggestions... I'll start researching those immediately. I hadn't even thought about bamboo. It is pretty invasive, but worth considering.

The cistern will be concrete. Right now I have it located along the setback line (the front of the house). I don't think I want a big concrete cistern hard mounted to the house-on-stilts. My thinking is that in strong winds the house will move a bit on the truss. The cistern would be anchored to the ground, and so I think the joint between the cistern and house would get stressed. Plus, at the setback line the cistern would have to be at least 10 ft high to connect to the house. So, I think of it as a closed in pool, under the house. I'll leave about 5 ft sticking out from under the house (to the side) so that if I get water delivered, there is easy access.

You're right about not needing much shade for north facing decks. But, I have the sun charts now (thanks heepajeep), and I can see that there are a few weeks in the summer when the Sun gets north of nadir (it should be now). I might just use umbrellas, but of course trees provide a really nice dappling effect, and in the breeze it's wonderful movement. If I get too many tall trees I'll block the breeze, so I'll have to find the right balance and placement.

I haven't been to the Ag Station... I think that's at the University, right? I'm making a list of all the things I want to do on our next visit, so I'll add that.

I think I'll try to hire an architect or real estate agent to take me around to see examples of houses on steep lots/stilts, different building materials (Tridipanel, thermasteel, RASTRA, etc), trees, solar panels, wind generators, fruit and vegetable gardens, etc. In between the sunburn of snorkeling, beach lounging and sailing, it would be a nice break.

I just discovered the Calabash Tree... and what a find this was!

It grows to 30 ft, and is often clumped (multiple trunks) - my kind of handsome tree! So, architecturally it sounds similar to Crape Myrtles.

But, it doesn't end there. There are stories of:
- people using the large, round fruits/gourds as bowls
- marakas are made from these gourds
- better yet:
---- hunters would make helmuts that went below the eyes
---- then, they'd cut eye holes in helmuts
---- walk out into the ocean so that only the helmut showed
---- birds would be fooled and land close to the gourds
---- snatch them by the legs... and a tasty stuffed seagul dinner!
- so, I'm thinking that from this one plant and a couple of capes I have the start of a superhero maraka band, with bird hunting on the side!

OK, enough dreaming... anyone have one of these trees? Any nasty drawbacks (ie, do the trees attract wasps or fire ants like there's no tomorrow, or smell like rotting flesh, or have chemicals that do rot flesh)?

If you are very careful when clearing the land to leave behind what does not need to be removed, the natural vegetation will grow up rapidly. Paint the columns a dark color so they don't stand out.
So many people go onto a piece of land and strip it clean of trees that have been growing naturally for hundreds of years, then ponder what they can put in that will grow, when they had it all before they cut it down! The existing stuff does not need to be watered either!
I have been to a brand new house here in St Thomas with vegetation around it that the owner made sure to it that they did not touch the trees that were not in the way. The place looks so landscaped, but it's brand new! He did have to fire his first bulldozer guy because he would not give in to the idea of not stripping the land bare.

I have the same beliefs as Ronnie, especially on the watering issue.

Thanks Ronnie,
I hear you. One of the other reasons that I want the house on stilts is to disturb the land as little as possible; mostly because I'm worried about land erosion from rain. Exposed soil on steep land will wash away in no time and create ruts that will perpetuate the erosion. Luckily, even if the construction does end up clearing land, I think I can persuade soil hugging grasses and shrubs to come back quickly (just keep throwing grass seed out during the construction).

I had been thinking of an umber like color for the truss to blend in with tree trunks, but maybe a black would blend into shadows better.

And... there are only a few trees on the lot (nowhere near the house location). Mostly there are medium height shrubs that just aren't high enough to hide the 20 ft trusses. It might be that if some of the brush were trimmed, that maybe there are smaller trees that might have a better chance of reaching some height. I'll have to assess that.

Just found this site... looks promising:

http://www.usvircd.org/STXEIR/STXplants.htm

I am having a problem visualizing exactly what your construction will be. When you say 20' steel truss do you actually mean a 20' steel post? A truss is an engineered structural member used to bridge a gap and in residential construction you would normally use them in place of floor joists or rafters.

If in fact what you are talking about is a post then has the structural engineer taken into account both the positive and negative loading these posts will have to deal with in a hurricane. If it were my home I would be concerned with the wind getting underneath the floor and lifting the home off its footings.

Also before planting anything to close to my home, particularly at the top of a ridge I would consider what will happen if a brush or grass fire sweeps up the hill? On STX during the dry seasons brush fires are not that unusual.

Jim

Thanks Jim Dandy,

Let's see if I can paint a better picture:
- imagine a 1:2 slope, where there is a road at the high end of the slope.
- go horizontally out from the road, 20 ft. That is the edge of the setback, and that is where the bottom front of the house would be.
- continue horizontally out another 20 ft, and that is where the bottom back of the house will be.
- so, you can see that the house is 20 ft "deep". It is 80 ft long. Only one story.
- with a 1:2 slope, the front of the house is roughly 10 ft above ground, and the back is roughly 20 ft above ground.
- so, the entire house is off the ground
- the steel truss is made of steel vertical beams with horizontal and diagonal joining steel beams. This truss forms a grid under the entire house, and also under the driveway (the driveway connects the house to the road, on the same horizontal plane as the house).

If the house floor is concrete (1600 sqft) and the truss grid is open on all four sides of the house then I'm hoping that the winds will travel under the house without building sufficient pressure to raise the house off of the post foundations. I'm still researching this issue.

The cistern complicates the picture a bit: it is probably 40 ft wide, 8 ft high and is located under the highest front corner (but, again not structurally connected to the house). And I haven't talked about a deck or septic field, but this is the basics.

I was going to someday ask about the prevalence of brush fires... thanks. I think the steel trusses would be OK, and a concrete floor will be OK, and I plan on Tridipanel, RASTRA or thermasteel for walls so I think that is OK. But, good point - I might be better off keeping the trees below deck level.

You need to get someone who can do wind speed calculations when designing the structure. With the square footage you have assuming a load of 60 psi that is 14 million pounds of wind load your structure will need to be able to handle. Because of the height you will also have to stabilize it for the earth tremors we get here on a regular basis.

As for fire it doesn't make any difference fi the materials are fire proof.. If heat from a fire gets trapped under your structure the steel posts and trusses will expand and distort and your structure may collapse. That is why in a commercial steel structures they insulate the steel to protect it from a fire's heat and prevent the building from collapsing at least long enough for the occupants to escape.

Hire your structural engineer before you worry about the landscapping.

Jim

Thanks Jim Dandy,

I appreciate your thoughts and the calcs and specs. I'm definitely in the conceptual stage of design. So, I'm trying to get info on all of the issues in order to make design decisions. I have a starting design that allows me to ask what if questions. As I get answers, and understand the issues better, the design will morph accordingly. I'll be talking to a steel/welding company in the next few weeks.

I think you need to have your structural engineering done before you begin worrying about the landscaping.

If hurricane strength winds get under your floor you need to be able to withstand large loads. For instance your 1,600 floor, if it has to withstand 60psi, this translates into approximately 14 million pounds. They test doors in Florida to 90 psi. The structure also needs to be able to withstand the regions frequent earth tremors. I think the shake we had last week was in the mid fours.

As for fire, the problem with your structure won't be it burning, but the heat trapped under the floor from a grass fire causing the steel structural members to expand and warp. This could cause your posts and trusses to fail.

Good luck with your design, it sounds like an interesting way to get best use out of your site.

Jim

Jim,

I'm not sure I understand your 60 PSI wind load number. I just did a little research and got:
- windload (PSF) = WindSpeed(knots)2 * 0.00431
- since (PSI) = PSF/144
- then windload(PSI) = WindSpeed(knots)2 * 0.00431/144
- for a 300 knot wind, PSI = 3002*0.00431/144 = 2.7

So, with 200 knot winds, 6" thick concrete, 1600 sqft of floor area and 150 lbs/cuft for concrete I get:
- weight of floor = 120klbs
- force of wind on floor (assume 45 deg strike angle): 195klbs
- so, the rest of the house might add the required additional weight, or I need to make the floors a bit thicker.

Have I done something wrong here?

Yes, I understand your point about the heat warping the steel truss... that would not be good. I'll have to research the temp vs duration that these trusses can handle, and then see if the land (plant fuel supply) around it can be managed. Like I said, I'll be contacting the steel folks in the next few weeks... I'll see what they can tell me about these topics (weight load, temp vs duration, earthquakes).

I can't tell you if your calculations are good or not. Not an engineer. I do know that for a door to be Dade County approved it must hold at 90 psi as well as pass the 2 x 4 test.

The challenge with your structure, as I see it is that it must withstand both positive and negative forces. Air pressure pushing up from underneath and/or pressure pushing down from the top. You also have to resist the forces pushing on the side of the structure facing into the wind. You are going to have to model the loads using some fairly sophisticated software to come up with a sound structure. Earth quakes just make it just that much more complicated to design the framing.

The fire heat problem can be managed by good common sense as long as you are aware of the potential problem.

Jim

I think I see the problem. I think the load ratings are in PSF (pounds per square foot) not PSI (pounds per square inch).

So, the door has to survive 90 PSF. For a 7 ft x 3 ft door (21 sqft), that would be a load of about 2000 lbs (pretty hefty).

If the rating was 90 PSI, then that same door would have to handle 144*2000lbs = 144 tons... not very likely.

So, I think my numbers are correct... but your basic assertion is still correct: the wind load trying to lift the house is very significant, and I have a bit of a problem right now.

I live on STT and the guy across the street from me finished building his house in 2005. Since construction ended he has had two to four water truck deliveries each week. This water goes into a cistern separate from the house and is used solely for landscaping because, according to the caretaker, the house cisterns can't keep up with the water needs of his landscaping.. Sure, what landscaping you can see behind the gates looks attractive, but the owner has not been to this house in almost two years so only the caretaker, who lives in Bovoni, ever sees the lush and colorful gardens. If money matters for your project, try to protect the plants that are already on the lot.

What a total waste!!

Talking about plants... cause I know nothing about the structure side of this topic...

I have lots of trees and I love flowering trees. Here are my favs:

Flamboyant. Right now our island has just come ablaze with Flamboyant trees... aka Royal Poincianas. Orange Orange everywhere and some yellow too. They are fast growing... I planted several on my property in last 5 years that are now over 20' and they have beautiful trunks. They do drop pods, and lose their leaves yearly but somehow they don't bother me much. Just part of "fall". Great shade, bloom in summer. I have planted the hot pink Bouganvilla at the base of mine and the Bouganvilla has climbed the tree and offers its dark pink red blooms throughout the year. It looks awesome.

African Tulip. Also a beautiful Orange Flower. Blooms multiple times per year. Fast Growing.

Mahogany. Very popular on island, slower growing. Massive. It is illegal to cut one of these mature trees down without permission from the govt, believe it or not. I have a love hate relationship with mine as they shed their leaves and drop heavy pods. Mine came with the property and are too close to the house so they make a mess of my pool deck and drop pods on my roof which sometimes makes me jump... but, when they are not shedding, I love them. They offer a lot of shade and have a beautiful trunk "style".

The Tourist Tree. AKA Turpentine tree. This tree is by far the most beautiful in my book because of its red trunk. They are called tourist trees because their skin turns red and peels off. 🙂 They are extremely slow growing. Please don't ever clear one. These trees are a treasure. Beautiful smooth skin.

Banana Trees, or Plantain. This is a great thing to have on property. they should be planted in bunches, the trees easily grow to 15/20 feet and the plantain ones grow taller I think. My most productive "clump" is fed by shower water drain off and never is without a stalk of bananas of 6 or 7 hands. They are gorgeous and green, but they must be cared for and the old stalks removed to let new ones come in. Very tropical. I also love my ginger plants and elephant ears but they are shorter landscaping plants. Think water. Unless you have plenty of cistern water or live in the rain forest... don't consider these.

Bamboo... takes a lot , lot , lot of water too. It is absolutely beautiful in Puerto Rico along the rivers... but I don't think it really grows that well here. But that may just be me.

Don't forget Palms... Travelers, Royal (very tall and elegant), Coconut. Nice to look down on from your patio.::)

I could rattle on forever... and have been known to... so I guess I'll just end it here. Good luck with your building. Don't build a kite that will fly away in the wind... the tendency here is to never build with big overhangs.