Is it necessary to have ceiling vents to allow air circulation?

[ubonr1971]

Im renovating the top floor of our building. The old gyprock ceiling has been pulled out. The new aluminium structure is still in place ready for the new ceiling. I intend to buy insulation bats to lay down before the new ceiling is installed. 

 

I have just finished closing all gaps in the ceiling to prevent water coming in. On a previous house of mine back home I remember putting in a few vents to allow fresh air to come in. Is this absolutely necessary? Whats the purpose? If I dont do it..... any issues down the track?

 

thanks

[bankruatsteve]

I've seen that in homes 100 years old.  No windows to open?  Where would fresh air come from above the ceiling?

[Morakot]

43 minutes ago, ubonr1971 said:

closing all gaps in the ceiling to prevent water coming in.

I'm sure something got lost in translation here...

 

 

Are you talking about roof vents?

[ubonr1971]

6 minutes ago, Morakot said:

I'm sure something got lost in translation here...

 

 

Are you talking about roof vents?

yes. and there's also the square shaped ones that one can install on the vertical wall in the roof. Are they necessary

 

[scorecard]

2 minutes ago, ubonr1971 said:

yes. and there's also the square shaped ones that one can install on the vertical wall in the roof. Are they necessary

 

My investigation on this point is that some form of ventilation is needed to get the very hot air out of the roof cavity, otherwise the upstairs rooms will be quite hot from heat soaking down from the hot air in the ceiling plus the upper level room closest to the sun will be super hot. 

 

Further the professionals on this subject seem to suggest ventilation to get the hot air out and ventiliation to allow cooler air to get in.  

[Morakot]

13 minutes ago, ubonr1971 said:

yes. and there's also the square shaped ones that one can install on the vertical wall in the roof. Are they necessary

 

 

Not strictly necessary, but may improve the situation if there's a lot heat retention. 

 

If you have a gable roof, you should go for gable vents. It's an infinitely better solution.

 

 

[johng]

@ubonr1971   is it the same  mouldy room  as your other thread   with the "not enough" overhang roof ?

 

[ubonr1971]

54 minutes ago, johng said:

@ubonr1971   is it the same  mouldy room  as your other thread   with the "not enough" overhang roof ?

 

yes

[eyecatcher]

Vents are pointless because hot air in the roof is the same as the hot air outside, extract one amount and another amount replaces it.Even a jet powered fan system has no effect unless you replace that air with cool air.

Think about it.

 

Soffit vents in the west are there for the purpose of circulating air and allowing humidity not to increase moisture levels of timber roof trusses and ceiling joists.

Airbricks at ground level are doing exactly the same job.

 

In Thailand steel trusses and concrete floors do not need ventilation.

[BritManToo]

6 minutes ago, eyecatcher said:

Vents are pointless because hot air in the roof is the same as the hot air outside,

Disagree, in the early evening the roof space air is way hotter than the outside air.

[bluejets]

16 hours ago, Morakot said:

I'm sure something got lost in translation here...

 

 

Are you talking about roof vents?

Those things are useless..........wouldn't pull the skin off a rice pudding.

 

 

Far better ( proven on many occasions) to use a few 6" vertical vent pipes with a vent "hat" on top.

Works 100 times better.

Install on roof high point (obviously just below ridge capping)

 

Put some intake vents in the suffit to feed the above vents.

 

[Rickyoz]

Depending upon the diameter of the vents and the wind speed outdoors, the turbines can expel vast quantities of humid air before it becomes a problem. A small 12-inch-diameter turbine vent with a constant wind speed of 5 miles per hour (mph) can remove 347 cubic feet of air per minute (cfm) from the attic space.

A single 14-inch-diameter turbine vent that is subjected to 15 mph winds can expel up to 1,342 cfm of air! If the winds are still, the vents still allow air to drift up and out of the attic space, although not nearly as much.

 

So, if a 6 inch vertical pipe works a 100 times better, then it must move a 100 times more air. With no turbine assistance, with a diameter less than half that of the turbine vent, the plain pipe has to exhaust at least 347,000 cfm of air from inside the attic space. Wind speed has no bearing on this requirement. Patently impossible.

 

Soffit vents are needed, otherwise almost no air can be removed, Air in the attic space heats up with sunlight on the roof, and, if not removed and replaced with cooler outside air, soaks through the ceilings, even with good insulation, heating the upper floor. The vertical pipes do work, but actually, are less efficient than the turbines, although cheaper.

[fredge45]

Roof vents and soffit vents to allow incoming air.  Works just great.

 

I have used both fixed and rotating roof vents - the latter only because it made the total unit a bit cheaper.

[rwill]

No they are not necessary.  Many homes here do not have them.  But they can help remove heat from the attic space.

 

 

[4MyEgo]

19 hours ago, Morakot said:

 

Not strictly necessary, but may improve the situation if there's a lot heat retention. 

 

If you have a gable roof, you should go for gable vents. It's an infinitely better solution.

 

 

Yes the vents for a gable roof with the whirlybirds create a beautiful wind tunnel, and those birds spin 24/7, sucking that hot air out.

 

You cannot go wrong with the saloon style vents just under your gable roof (facade), don't forget to also put soffit boards under your eaves for ciculation, and put the whirly birds at either end of the roof away from the vents and R38 stay cool batts and you will see the difference.

[holymoly]

Without ventilation, the roof cavity will get extremely hot and will heat the room below.

 

Good ventilation requires opening underneath the soffit , maybe two per side. Also an good outlet on top of the roof. I come from Canada. Sellers of a/c units frequently will refuse to install a/c unless the roof ventilation has been properly installed.

[4MyEgo]

2 hours ago, bluejets said:

Those things are useless..........wouldn't pull the skin off a rice pudding.

That's a big statement saying whirlybirds wouldn't pull the skin off a rice pudding.

 

Come over to my place and stand under my whirlybirds and you WILL feel them sucking the air out of my roof space, that said, with a gable roof high enough to stand in, having ample vents at the front, side and rear and soffit boards under the aves, it creates the perfect wind tunnel to keep my house cool all day and night.

 

I stand by whirlybirds, but on their own, they depend on the wind to spin them, do the above and you create your own and they spin 24/7.

 

The R38 batts do also do a great job in reducing the hot air from coming through, add to the underside of the roof tiles sisalation which helps to also reduce the heat coming into the ceiling space on top of the R38 stay cool batts.

[Mattd]

12 hours ago, eyecatcher said:

Vents are pointless because hot air in the roof is the same as the hot air outside, extract one amount and another amount replaces it.Even a jet powered fan system has no effect unless you replace that air with cool air.

Think about it.

The air inside the roof space is degrees warmer than the outside air, by some considerable margin, the heat is radiated in to the space from the roof, which is then exacerbated by the lack of movement, don't believe me, then try going in to the attic for a while!

At least if the space is ventilated it allows some of the hotter air to escape and creates movement.

[AAArdvark]

12 hours ago, eyecatcher said:

Vents are pointless because hot air in the roof is the same as the hot air outside, extract one amount and another amount replaces it.Even a jet powered fan system has no effect unless you replace that air with cool air.

Think about it.

 

Soffit vents in the west are there for the purpose of circulating air and allowing humidity not to increase moisture levels of timber roof trusses and ceiling joists.

Airbricks at ground level are doing exactly the same job.

 

In Thailand steel trusses and concrete floors do not need ventilation.

The first part is completely wrong.  

[The Theory]

Air circulation is needed for any roof, anywhere. If you see lack of it in some buildings it does not mean that "not needed". Contractors want to cut the cost. There different ways to make circulation under the roof. But anyway you do, do it right and prevent roof leak that will be a headache. Never trust Thai contractors unless the plan makes sense to you. Watch them closely otherwise they just want to finish (Lousy work) it and go for evening beer party. 

If your house top floor has a dead hallway (at the end of stairway) with doors to bedrooms without any windows then I suggest you to install an ceiling exhaust fan at the best location since heat gets stuck up there under ceiling and makes it like a sauna (very common in Thai style 2 or 3 story attached/detached houses. 

[The Theory]

21 hours ago, ubonr1971 said:

I intend to buy insulation bats to lay down before the new ceiling is installed. 

Without air circulation under the roof insulation won't work perfectly since the heat get stuck under the roof and eventually makes the ceiling warm. Insulation's work to stop heat radiation from roof, but air circulation still needed.  
 

 

[AlQaholic]

If your house is two floors high, it makes sense to have vents, preferably protected from water ingress. because of the slight air pressure difference between the bottom floor and the location of the vent, there will be a natural flow of air from the higher pressure at the bottom floor to the vents which are located at a lower air pressure.

[brianthainess]

4 hours ago, bluejets said:

Those things are useless..........wouldn't pull the skin off a rice pudding.

 

 

Far better ( proven on many occasions) to use a few 6" vertical vent pipes with a vent "hat" on top.

Works 100 times better.

Install on roof high point (obviously just below ridge capping)

 

Put some intake vents in the suffit to feed the above vents.

 

Also the spinning ones can become noisy, squeaking and rattling away.

[willi2006]

I'm afraid there's no simple answer. It depends on the details.
Ventilation against humidity: Some gaps will do the job.

Ventilation against heat. The roof space is heated up by sun radiation, similar to a closed car parked in the sun. Opening the windows will help. But parking in the shadow under a tree or carport will help more. I measured up to 70 °C in our roof space.

Questions to answer:

• Is the temperature between roof space and outside on top of the roof enough to drive the roof vent?
• Is there enough wind to drive the roof vent?
• Is there a motor to drive the roof vent?
• Where does the incoming air is taken from? Is it cool enough to do the job?
• Is the air flow rate high enough to get the temperature down?

[chilly07]

Always ventilate roof voids via eaves soffits not ceilings. Never insulate roofs in hot climates as this retains heat and is usually a fire hazzard.

Thais adoption of concrete clay tiles and bricks and glazed windows thus requiring universal comfort cooling should be compared to old style teak building with steep roofs no ceilings louvres instead of walls where no cooling is required other than ceiling fans. Raised on concrete columns to prevent termites of course. 

[ubonr1971]

48 minutes ago, chilly07 said:

Always ventilate roof voids via eaves soffits not ceilings. Never insulate roofs in hot climates as this retains heat and is usually a fire hazzard.

Thais adoption of concrete clay tiles and bricks and glazed windows thus requiring universal comfort cooling should be compared to old style teak building with steep roofs no ceilings louvres instead of walls where no cooling is required other than ceiling fans. Raised on concrete columns to prevent termites of course. 

'Never insulate roofs in hot climates as this retains heat and is usually a fire hazzard.'    are you saying that its a fire hazard to lay down insulation bats in the roof? I dont understand

[khunPer]

23 hours ago, ubonr1971 said:

Is this absolutely necessary? Whats the purpose? If I dont do it..... any issues down the track?

Yes, it's necessary with ventilation – good ventilation – not to damage the house in various ways, including growing fungus.

 

Over insulated houses in cold areas – like my Scandinavian home country – are huge problems; have to be done right with correct moisture membrane and ventilation, not to damage the building.

 

You don't need the ventilation to be in the roof, it can also be in the house gables, just it gives a good ventilation. I made that in my house, together with ventilation grilles under the eaves, it works perfect.

 

 

Remember to have an insect net in any ventilation openings; some of the ventilation grilles comes default with an insect grille, if not, make sure to install one.

 

In old-time Thai houses – before the aircon-era – all houses had ventilation under the ceiling, you can easily spot the ventilation structures in both older wooden and concrete buildings. It works both for cooling down from airflow, and for structure ventilation.

[sometimewoodworker]

1 hour ago, chilly07 said:

Never insulate roofs in hot climates as this retains heat and is usually a fire hazzard.

Completely untrue.

[The Theory]

"Always ventilate roof voids via eaves soffits not ceilings. Never insulate roofs in hot climates as this retains heat and is usually a fire hazzard." 

I'm not sure what means: "never insulate roofs" ! Anyway, there is a gap between under roof insulation and roof materials for  air circulation purpose. Only if insulation material is sprayed foam/pre sprayed foam there will be no circulation space between. 

Insulation laid over ceiling is more common. That reflects heat radiation away from ceiling, but the heat must be vented, not trapped inside closed space above ceiling. 

[Moonlover]

16 hours ago, eyecatcher said:

Vents are pointless because hot air in the roof is the same as the hot air outside, extract one amount and another amount replaces it.Even a jet powered fan system has no effect unless you replace that air with cool air.

Think about it.

 

Soffit vents in the west are there for the purpose of circulating air and allowing humidity not to increase moisture levels of timber roof trusses and ceiling joists.

Airbricks at ground level are doing exactly the same job.

 

In Thailand steel trusses and concrete floors do not need ventilation.

Trust in ancient wisdom. Look up at any of the teak dwellings in a village and you will see louver vents in the gable ends. They are there for the express reason of allowing hot air to vent out of the roof space. Hot air rises and escapes through the vents, allowing cooler air in below.