Some schools are considering using mobile homes or log cabins as isolation areas for students.
Ann Piggott is president of the Association of Secondary Teachers Ireland (ASTI).
She says schools are preparing to take students back in the coming weeks.
She told Pat Kenny a lot of work is going on behind the scenes, but available space is a big concern.
"At the moment, a lot of work is going on in terms of preparing the physical brims in schools.
"Classrooms are changing, different numbers will be in rooms, people will be kept in different areas.
"Teachers themselves probably still haven't got their final timetable because timetables would have changed because of that.
"Teachers are in school at the moment, emptying out their classrooms and they're spending days in there taking out 20 and 30 years of their work and their lives.
"So members are getting ready in that way".
She also said that a lot of members are actually returning to work next week.
Posters are to be made available for advice to teachers and staff - but these are not yet available.
"As far as I know the posters are going out to schools quite soon, and they probably are landing there this week," she said.
In terms of creating extra space, she said: "Some schools have ordered prefabs, and I think they're probably more expensive than they used to be.
"And likewise, a lot of schools would have thrown out their big desks and got smaller desks - individual desks".
"Space is at a premium, particularly in older schools - some principals that I was talking to were even considering getting mobile homes or log cabins so they can use [them] as isolation areas for students when the need arises.
"It is very difficult to find all of the room, but areas such as PE halls, assembly areas... staff rooms actually have disappeared and some staff rooms have turned into two and three classrooms.
"So every inch of available space is being used".
Referring to the plan for re-opening schools, she said: "Schools are probably going to try and use different doors, so parents might be able to use different sides of schools or different roads to drop off their children.
"On buses, children will be expected to wear the masks, they will also be given an assigned seat and they will also be required if possible to sit with a brother, a sister or somebody in their own class group."
On school uniforms, she said: "I don't think there's any advice on uniforms.
"I think some schools at the start when they were getting ready were suggesting that students and parents would wash their uniforms every day: now that's not possible.
"But if you do go into a shop, for example and try on clothes, they keep them aside and they steam them - or advice has suggested maybe ironing your masks at 60 degrees might kill any virus.
"Now, not being a health expert, but I don't know how long a virus might live on clothing.
"But I don't think there's a big focus on uniforms, I think that might be considered OK.
"But objects such as pens, lunchboxes, shared markers - they would be of concern.
"I am actually getting a lot of phone calls from teachers of subjects like engineering and arts where students would have to share equipment.
"So a lot of schools might have two drills, or might have 12 vices in a classroom that students would have to share.
"And they would obviously have to be washed down and sanitised between every single [class]."
On private schools not getting access to the funding, Ms Piggott said: "I think they have a valid point and their students need to be protected.
"I suppose the point is that private schools might charge fees and might have money that other schools don't have.
"I did hear the minister responding to a question on this, and the minister did state that the schools would not be deprived of the funding - but they need to show that they need the funding.
"So schools like that should get their applications in as soon as possible and I would expect that they would not be refused should they need the money".