How to DIY Your own Bio Roof
If you have a flat roof and its more than a few years old- Go take a close look at it in most cases you will find some moss or lichen – So you already have the start of a bio roof. In order to promote more diverse growth you need to increase the organic matter, Make sure you don’t block the drainage & stop it from drying out.
There are many companies now offering to transform your ugly roof into a wonderful vista of wild flowers and mosses. Don’t get me wrong I love the idea but let’s first consider the facts.
This is something you can DIY. It’s not rocket science.
This green roofing option is only suitable for roofs that have Asphalt, felt, GRP, or a single ply membrane-waterproofing system.
If your roof has a metallic covering- like lead, Copper or stainless steel. Go back and watch top gear or buy some pot plants.
Most importantly adding anything to your roof increases the weight- although many of the schemes are based on lightweight materials. The first job on the list is to calculate the added weight and make sure the structure of the roof can support it. Most well constructed roofs will be able to cope. For a rule of thumb, go up on the roof stand in the middle of your roof and jump up and down. If doing this leaves you with a feeling, I’m pleased I did not jump harder. Best get it professionally checked out. Assuming it left you with the feeling – I’m going to have a party up here in the summer. It’s probably ok. A simple green roof will weigh between 60-200kg per m2- that’s like having a very obese person standing 1m apart in every direction.
Condition of your roof
Next- How good is the water proofing. It needs to be in tip top order. Getting a leak after you just finished recreating a lost wilderness will leave you feeling suicidal.
Up-stands. – Most roofs have these it’s the bit where a flat roof joins onto an existing wall- or any elevation where the water is not supposed to run off. They should be a minimum of 150mm above the finished roof surface. If you add 150mm of growing matter it will come to the top of the up-stand and you will get a leak or have dirty water running down your windows- either have the up-stand height increased, or you will need to form a break gap along the effected sides.
That leads us nicely into -
You will need to stop your hard work from washing away and blocking the drains.
To do this a barrier is required to allow water to run through but not the organic material. There are commercially available grill systems to suit all depth requirements.
They need to be placed on all edges where the water is intended to leave the roof. Grills in stainless steel are best for this. Next is-
Unless you want to create a mud bog the rain water needs to be able to percolate through you new ecosystem and discharge into the drainage system.
Again commercially available drainage products designed for this are available. First a layer of pond liner EDPM 1mm thick membrane is fitted. Then the drainage system is laid over the whole area prior to loading up your organic matter.
Organic material & depth
Just getting the wife to haul buckets of soil up a ladder for you to distribute is not the way forward. Remember it needs to be lightweight. So you need to use a mixture of 70-80% inorganic matter like crushed brick, expanded clay. 20-30% organic matter- compost.
Depth- most DIY roofs need to have 80- 200mm of growing matter. This ultimately depends on what you want to grow. If it’s just moss, grasses or cannabis the minimum will do just fine. If you are seeking to be a little more adventurous and want to re-create a redwood forest then it’s back to the drawing board.
Keeping it moist (Such a nice word)
You’ve put in a lot of hard work and planning to get this far. From your bedroom window you can see -Wild flowers and ornate Grasses blowing gently in the summer breeze.
Then we get a dry spell & yes it will happen remember- (If you were in the UK) Feb to April 2012 right up until they announced the hosepipe ban- After that timely government announcement, it never bloody stopped raining.
So now you’re hanging out of the bedroom window with a hose pipe that will be surely leaking somewhere on your finest Axminster carpet.
Consider installing an irrigation system before you start.
If you allow the organic matter to dry out it becomes a fire risk.
The Germans have produced data on this and made recommendations about fire breaks etc. Seems Fritz is worried your going to burn the house down.