Read in conjunction with the post on walls for facade reinforcement.
Sandia research says:
floor of 8″ reinforced (0.5″ rebar on 12″x12″ centres) concrete lasts ?m against 4lb explosive and hydraulic boltcutter,
floor of carpeted 1.5″ plywood, over insulation held by chickenwire, lasts 54s against tinsnips and circular saw, or 48s against shaped charge,
roof of 5.5″ reinforced (no 4 rebar on 8″ x 12″ centres) concrete roof lasts 2m48s against 4lb explosive and 20lb boltcutter, if the steel sheet is replaced with 2.5″ concrete then a shaped charge takes 54s to get through,
roof of ribbed steel decking covered with 16 gauge steel sheet covered with 2″ insulation covered in 0.5″ asphalt & gravel lasts 2m18s against a 10lb fire axe and 5lb shovel,
ceiling of 4″ reinforced (no 10 6″x6 mesh) concrete, 0.25″ plasterboard and 0.75″ plaster lath on protected face lasts 2m 24s against a shaped charge, 10lb sledgehammer and 10lb boltcutter,
ceiling of 3.5″ insulation, 0.25″ plasterboard and 0.75″ plaster on protected face on metal laths lasts 1m against a 5lb fire axe,
American prison research found that roofs were made of 22 gauge (0.7mm) steel sheet and 2 or 3 inches of concrete and only lasted 3-4 minutes against axes, boltcutters and sledgehammers, partly because reinforcement was only no 10 wire in 6” squares or no3 rebar on 18” centres.
According to the US DoD navy security design handbook:
Wood floors and ceilings should see off light hand tools but can only last about 1.5 minutes against heavy hand tools or battery or power tools.
Metal roofs last about 2 minutes but metal floors can last 15 minutes if a riveted steel grating is used.
Steel plate 6mm floors effectively require power tools, which you can resist by adding layers of plywood and steel plate.
Steel grate floors will not stop power tools for a minute but should stop battery tools and heavy hand tools.
Expanded steel mesh grate floors only last a minute whatever levels of tool is used.
Concrete floors can last 45 minutes and concrete ceilings can last 35 minutes against high threat tools and should see off heavy hand tools and battery tools.
Concrete floors at least 12” thick become much harder to penetrate as reinforcement increases, but if the reinforcement is mesh then it does not make much difference.
You can buy an extra 9 minutes against medium threat tools by bolting 9 gauge (3.7mm) steel expanded mesh to the protected surface of a reinforced concrete floor or ceiling, or you can double penetration time of reinforced concrete by bolting 10 gauge (3.2mm) steel plate to the protected surface. You can then go even further with either steel grating or layers of plywood and steel plate.
Sandia recommend any secondary roof be about 10” below the original one to make it harder to fit tools between.
Roofs can be built as for walls, but due to the assistance of gravity need extra strength. Concrete roofs need an extra inch of concrete or rebar two sizes higher. In contrast, gravity works against upward attacks on ceilings, so if that is the avenue of attack then you can subtract an inch of concrete thickness or two sizes of rebar.
US military specification for delays from roofing materials as per the five levels in the ‘walls’ post are:
Level I – very low
Thin plywood or less is level 1 very low protection.
Level II – low
1 minute (also up to level V for non-explosive attack) delay from ¾” plywood on wooden joists.
2 minutes (also level III) from 20-24 (0.5-0.8mm) gauge sheet metal (insulation on top may slow down tools),
3 minutes from 16 gauge (1.34mm) sheet metal,
3-4 minutes from 2-3” 3,000PSI concrete,
4 minutes (also level III) from 2” 3,000PSI concrete on 16 gauge (1.34mm) sheet metal,
5 minutes from gravel and rigid insulation over steel decking,
5 minutes from 2.5” 3,000PSI reinforced concrete on 22 gauge (0.66mm) sheet metal deck,
6 minutes from 4.5” ,000PSI concrete with no4 rebar each way on 18” centres on 16 gauge (1.34mm) sheet metal,
6 minutes from 5.5” 3,000PSI concrete reinforced with 10 gauge (3.1mm) steel mesh,
6 minutes (also 2 mins at level IV) from 3” 3,000PSI concrete reinforced with no10 6” steel mesh on 2.5” concrete planks,
15 minutes for 6” 3,000PSI concrete with no4 rebar each way on 8” centres on steel decking,
30 minutes (also level IV) for 8” 3,000PSI concrete with no 4 rebar each way on 8” centres on steel decking.
Level III – medium
Levels III-IV generally need reinforced concrete.
1 minute (also level IV) from gravel and rigid insulation over steel decking,
5 minutes (also 1 min at level IV) from carpeted 1.5” plywood on 3” silicate insulation,
5 minutes from gravel and insulation over 2.5” 3,000PSI concrete reinforced with 10 gauge (3.12mm) 6”x6” woven wire over 22 gauge (0.66mm) sheet metal deck with screen mesh 12” below,
5 minutes from 6” 3,000PSI concrete reinforced with 6”x6” welded wire mesh over (3.12mm) 10 gauge-reinforced steel decking,
6 minutes delay can be added to reinforced concrete by retrofitting a sandwich of two layers of 10 gauge (3.12mm) hot rolled steel and one layer of 0.75” plywood, with each extra 22mm laminate of steel and plywood adding 5 minutes delay,
7 minutes from 22 gauge (0.66mm) steel sheet with insulation and gravel,
10 minutes from gravel and insulation over 2.5” 3,000PSI concrete reinforced with 10 gauge (3.12mm) 6”x6” woven wire over 22 gauge (0.66mm) sheet metal deck with screen mesh 8” below,
14 minutes delay can be added to reinforced concrete by retrofitting a sandwich of two layers of 9 gauge (3.5mm) ASTM A1008 class 2 high strength low alloy steel and one layer of 0.75” plywood,
15 minutes from gravel and insulation over 2.5” 3,000PSI concrete reinforced with 10 gauge (3.12mm) 6”x6” woven wire over 22 gauge (0.66mm) sheet metal (doubtful as specification gives shorter delay if additional mesh added below),
15 minutes from 10” 3,000PSI concrete with no5 rebar each way on 6” centres on steel decking,
20 minutes delay can be added to reinforced concrete by retrofitting a sandwich of two layers of 9 gauge (3.5mm) ASTM A1008 class 2 high strength low alloy steel and one layer of 0.75” plywood and a layer of 0.9lb per square foot gravel finish roofing felt either side of the plywood, plus you can add 100% of the concrete’s delay time due to the anti-spall effect,
26 minutes from gravel and insulation over 4” 3,500PSI concrete with no 4 rebar one way on 6” centres over exmesh over 22 gauge (0.66mm) sheet metal,
29 minutes from gravel and insulation over 4” 3,500PSI concrete with no4 rebar each way on 6” centres over 22 gauge (0.66mm) steel sheet,
30 minutes (also level IV) from 10” 3,000PSI concrete with two layers of no5 rebar each way on 6” centres on steel decking.
Level IV – high
12 minutes (also 11 mins at level V non-explosive) from 8” 3,000PSI concrete with no4 rebar each way on 9” centres,
23 minutes (also 22 mins at level 5 non-explosive) from 12” 3,000PSI concrete with no5 rebar each way each face on 6” centres.
Level V – very high
Level V blast protection generally needs 5,000PSI reinforced concrete sacrificial or bunker-thickness roofs. However, you should ensure any sacrificial barriers stand up to lower threat levels so they cannot simply be virtually instantly eliminated.
1 minute from gravel and insulation over 4” lightweight concrete with no5 rebar on 8” centres on steel decking,
1-2 minutes from 8” 3,000PSI concrete with no4 rebar each way on 9” centres,
2 minutes from 4.5” ,000PSI concrete with no4 rebar each way on 18” centres on 16 gauge (1.34mm) sheet metal,
2-3 minutes from 12” 3,000PSI concrete with no5 rebar each way each face on 6” centres,
5 minutes from 10” 3,000PSI concrete with two layers of no5 rebar each way on 6” centres on steel decking,
15 minutes from 10” 3,000PSI concrete reinforced with 5/16” exmesh on 2.5” centres on steel decking,
30 minutes from 12” 3,000PSI concrete reinforced with 5/16” exmesh on 2.5” centres on ¼” steel decking.
Beware roof installations with penetrations. These ready made holes need protecting by ensuring they are smaller than 96 square inches with maximum dimension 6”, or covering with a barrier or grille.
Reinforced roof exhausts with 0.5″ bars on 6″ centres through sheet metal can take about 4m to get through with explosives, sledgehammer, saw and chisel. Louvered sheet metal port aircon filter frame banks can take about 30s to get through with a 2lb crowbar.
Beware flat roofs creating hiding spaces. Railing instead of parapets help prevent concealment. Pitched roofs are safer for a given strength as they are harder to work on.
To protect against dangerous fragments from blast up to 2.7m/kg0.33 you can line light ceilings and roofs with 1mm steel. This will make them safer than untreated unreinforced masonry.
You can secure your own roof with security wall panels which usually involve mesh and plywood, although it works better during construction as you ideally need panels on both sides of the joists.
Even 8mm plywood or low rating exmesh under the roof will at least stop a burglar just ripping off tiles and diving in headfirst if you can get equally strong fixings.
Avoid sun tunnels over 14” wide.
To be sure of equivalence to SR3 you would need 0.5” steel and 0.75” plywood which a roof and loft will not take, so unless you want to install additional steel trusses you may have to accept thinner plywood and one layer of exmesh, perhaps on one or both sides of roof and loft to buy extra time.
BMI Icropal do Decra / Aerodek Robust Plus powdered stone-coated steel roof tiles to SR1 and SBD (by screwing steel bars between battens) but stopped selling them in the UK. They also do the SBD rated Formflash lead substitute flashing to disappoint roof thieves. Hambleside Danelaw do SBD rated GPR flashing and Dryseal roofing as an alternative to PVC.
Once the roof is on, your only option may to board up the inside using brackets to screw through the side of joists instead of the edge and bolt the boards onto the brackets. You could look atSecurilath or concoct your own equivalent with exmesh and plywood.
If you cannot save the roof then you are down the ceiling, which you can board over, such as in the loft, but then you face challenges like securing the loft hatch when no products are certified, and using an LPS padlock and hasp on a flimsy hatch and unprotected wood rafter is of likely limited use. The Access Panel Company do a communal loft hatch with lock for upwards of £80 which may be better than nothing.
Rooflights are available with SR ratings but only up to SR2, unless you want bars in which case they go up to SR3, but not many flat or tiled roofs are up to SR3 standard. SBD advice is to go for an SR2 rooflight or reinforce an SR1 rooflight with at least an SR1 grille.
Glazing Vision do their aluminium Skydoor / Skyguide / Skyhatch / Flushglaze Secure LPS2081 rooflights with 8.8mm laminated safety glass with 0.8mm PVB interlayer for SRA and 9.5mm laminated glass with 1.5mm ionomer interlayer for SRB, which start at about £1,000.
The Rooflight Company do their 3mm steel Neo Plateau SBD model (10mm P6B glazing) and SRB model (they say also has SR1 and 8.8mm laminated safety glass), and say their Conservation Plateau model comes in an SR3 version with bars and P6B glazing that needs a reinforced concrete kerb, and an SR2 version that goes in a hardwood or 5mm steel kerb. Many of their rooflights are at least SRA and their Secure+ range is SRB.
Duplus do their Part Q rooflights to LPS2081 SRA (Part Q+ is SRB) from £420 with 8.8mm laminated safety glass, although they also do SBD opening rooflights, and fixed walkon rooflights with glass at least an inch thick, from £1,500.